diff --git a/composer.json b/composer.json
index fd0a3a4b..bea3fa44 100644
--- a/composer.json
+++ b/composer.json
@@ -24,15 +24,17 @@
     ],
     "require": {
         "php": "^7.1",
+        "ext-dom": "*",
+        "ext-json": "*",
         "jean85/pretty-package-versions": "^1.0.3",
-        "phpunit/php-code-coverage": "^4.0||^5.0||^6.0||^7.0.2",
+        "phpunit/php-code-coverage": "^6.0||^7.0.2",
         "phpunit/php-file-iterator": "^1.0||^2.0",
-        "phpunit/phpunit": "^6.0.9||^7.0||^8.0",
-        "symfony/console": "^2.8||^3.0||^4.0",
-        "symfony/dependency-injection": "^2.8||^3.0||^4.0",
-        "symfony/event-dispatcher": "^2.8||^3.0||^4.0",
-        "symfony/process": "^3.3||^4.0",
-        "symfony/stopwatch": "^2.8||^3.0||^4.0"
+        "phpunit/phpunit": "^7.0||^8.0",
+        "symfony/console": "^3.4||^4.0",
+        "symfony/dependency-injection": "^3.4||^4.0",
+        "symfony/event-dispatcher": "^3.4||^4.0",
+        "symfony/process": "^3.4||^4.0",
+        "symfony/stopwatch": "^3.4||^4.0"
     },
     "require-dev": {
         "facile-it/facile-coding-standard": "^0.3.1",
@@ -41,8 +43,8 @@
         "phpstan/phpstan-phpunit": "^0.11",
         "phpunit/php-invoker": "^1.1",
         "php-coveralls/php-coveralls": "^2.0",
-        "symfony/expression-language": "^2.8||^3.0||^4.0",
-        "symfony/phpunit-bridge": "^4.1.3"
+        "symfony/expression-language": "^3.4||^4.0",
+        "symfony/phpunit-bridge": "^4.2"
     },
     "bin": [
         "src/Paraunit/Bin/paraunit"
diff --git a/composer.lock b/composer.lock
index 885be29c..f1e57721 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "e19719428d61713f5756222cc43da0cd",
+    "content-hash": "35bdc3f5b292dad3488b38c46baf0951",
     "packages": [
         {
             "name": "doctrine/instantiator",
@@ -4460,7 +4460,9 @@
     "prefer-stable": false,
     "prefer-lowest": false,
     "platform": {
-        "php": "^7.1"
+        "php": "^7.1",
+        "ext-dom": "*",
+        "ext-json": "*"
     },
     "platform-dev": []
 }
diff --git a/phpstan.neon b/phpstan.neon
index 26aecbdc..5cc3fa2f 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,14 +1,8 @@
 parameters:
     ignoreErrors:
         - '/does not call parent constructor from PHPUnit\\Util\\Printer/'
-        # needed with Symfony <3.3
-        - '/Call to function is_array\(\) with string will always evaluate to false./'
-        - '/Class Symfony\\Component\\EventDispatcher\\ContainerAwareEventDispatcher not found/'
         - '/Call to function method_exists.. with .Tests..BaseTestCase. and .assertStringContain.... will always evaluate to false./'
     excludes_analyse:
-        # needed with PHPUnit 6
-        - src/Paraunit/Parser/JSON/LogPrinterV6.php
-        - src/Paraunit/Process/ProcessBuilderFactory.php
         - tests/Stub/ParseErrorTestStub.php
 includes:
 	- vendor/phpstan/phpstan-phpunit/extension.neon
diff --git a/src/Paraunit/Configuration/DependencyInjection/CoverageContainerDefinition.php b/src/Paraunit/Configuration/DependencyInjection/CoverageContainerDefinition.php
index e20cca78..2c9b558d 100644
--- a/src/Paraunit/Configuration/DependencyInjection/CoverageContainerDefinition.php
+++ b/src/Paraunit/Configuration/DependencyInjection/CoverageContainerDefinition.php
@@ -33,13 +33,13 @@ public function configure(ContainerBuilder $container): ContainerBuilder
         return $container;
     }
 
-    private function configureCoverageConfiguration(ContainerBuilder $container)
+    private function configureCoverageConfiguration(ContainerBuilder $container): void
     {
         $container->setDefinition(PHPDbgBinFile::class, new Definition(PHPDbgBinFile::class));
         $container->setDefinition(XDebugProxy::class, new Definition(XDebugProxy::class));
     }
 
-    private function configureProcessWithCoverage(ContainerBuilder $container)
+    private function configureProcessWithCoverage(ContainerBuilder $container): void
     {
         $container->setDefinition(CommandLineWithCoverage::class, new Definition(CommandLineWithCoverage::class, [
             new Reference(PHPUnitBinFile::class),
@@ -54,7 +54,7 @@ private function configureProcessWithCoverage(ContainerBuilder $container)
             ]);
     }
 
-    private function configureCoverage(ContainerBuilder $container)
+    private function configureCoverage(ContainerBuilder $container): void
     {
         $container->setDefinition(CoverageFetcher::class, new Definition(CoverageFetcher::class, [
             new Reference(TempFilenameFactory::class),
diff --git a/src/Paraunit/Configuration/DependencyInjection/ParallelContainerDefinition.php b/src/Paraunit/Configuration/DependencyInjection/ParallelContainerDefinition.php
index 5d51b5a8..ae5a165e 100644
--- a/src/Paraunit/Configuration/DependencyInjection/ParallelContainerDefinition.php
+++ b/src/Paraunit/Configuration/DependencyInjection/ParallelContainerDefinition.php
@@ -19,7 +19,6 @@
 use Paraunit\Printer\SharkPrinter;
 use Paraunit\Printer\SingleResultFormatter;
 use Paraunit\Process\CommandLine;
-use Paraunit\Process\ProcessBuilderFactory;
 use Paraunit\Process\ProcessFactory;
 use Paraunit\Process\ProcessFactoryInterface;
 use Paraunit\Proxy\PHPUnitUtilXMLProxy;
@@ -32,11 +31,9 @@
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Definition;
 use Symfony\Component\DependencyInjection\Reference;
-use Symfony\Component\EventDispatcher\ContainerAwareEventDispatcher;
 use Symfony\Component\EventDispatcher\DependencyInjection\RegisterListenersPass;
 use Symfony\Component\EventDispatcher\EventDispatcher;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
-use Symfony\Component\Process\Process;
 
 class ParallelContainerDefinition
 {
@@ -69,7 +66,7 @@ public function configure(ContainerBuilder $container): ContainerBuilder
         return $container;
     }
 
-    private function configureConfiguration(ContainerBuilder $container)
+    private function configureConfiguration(ContainerBuilder $container): void
     {
         $container->setDefinition(PHPUnitBinFile::class, new Definition(PHPUnitBinFile::class));
         $container->setDefinition(PHPUnitConfig::class, new Definition(PHPUnitConfig::class, [
@@ -81,16 +78,9 @@ private function configureConfiguration(ContainerBuilder $container)
         ]));
     }
 
-    private function configureEventDispatcher(ContainerBuilder $container)
+    private function configureEventDispatcher(ContainerBuilder $container): void
     {
-        if (class_exists('Symfony\Component\DependencyInjection\Argument\ServiceClosureArgument')) {
-            $container->setDefinition(EventDispatcherInterface::class, new Definition(EventDispatcher::class));
-        } else {
-            $container->setDefinition(
-                EventDispatcherInterface::class,
-                new Definition(ContainerAwareEventDispatcher::class, [new Reference('service_container')])
-            );
-        }
+        $container->setDefinition(EventDispatcherInterface::class, new Definition(EventDispatcher::class));
 
         $container->addCompilerPass(
             new RegisterListenersPass(
@@ -101,7 +91,7 @@ private function configureEventDispatcher(ContainerBuilder $container)
         );
     }
 
-    private function configureFile(ContainerBuilder $container)
+    private function configureFile(ContainerBuilder $container): void
     {
         $container->setDefinition(TempDirectory::class, new Definition(TempDirectory::class));
         $container->setDefinition(Cleaner::class, new Definition(Cleaner::class, [
@@ -109,7 +99,7 @@ private function configureFile(ContainerBuilder $container)
         ]));
     }
 
-    private function configurePrinter(ContainerBuilder $container)
+    private function configurePrinter(ContainerBuilder $container): void
     {
         $output = new Reference(OutputInterface::class);
 
@@ -136,20 +126,20 @@ private function configurePrinter(ContainerBuilder $container)
         ]));
     }
 
-    private function configureProcess(ContainerBuilder $container)
+    private function configureProcess(ContainerBuilder $container): void
     {
         $container->setDefinition(CommandLine::class, new Definition(CommandLine::class, [
             new Reference(PHPUnitBinFile::class),
         ]));
 
-        $container->setDefinition(ProcessFactoryInterface::class, new Definition($this->getProcessFactoryClass(), [
+        $container->setDefinition(ProcessFactoryInterface::class, new Definition(ProcessFactory::class, [
             new Reference(CommandLine::class),
             new Reference(PHPUnitConfig::class),
             new Reference(TempFilenameFactory::class),
         ]));
     }
 
-    private function configureRunner(ContainerBuilder $container)
+    private function configureRunner(ContainerBuilder $container): void
     {
         $container->setDefinition(PipelineFactory::class, new Definition(PipelineFactory::class, [
             new Reference(EventDispatcherInterface::class),
@@ -167,7 +157,7 @@ private function configureRunner(ContainerBuilder $container)
             ->setPublic(true);
     }
 
-    private function configureServices(ContainerBuilder $container)
+    private function configureServices(ContainerBuilder $container): void
     {
         if (! class_exists('SebastianBergmann\FileIterator\Facade')) {
             \class_alias('\File_Iterator_Facade', 'SebastianBergmann\FileIterator\Facade');
@@ -186,16 +176,4 @@ private function configureServices(ContainerBuilder $container)
             '%paraunit.string_filter%',
         ]));
     }
-
-    private function getProcessFactoryClass(): string
-    {
-        // only reliable way to detect symfony/process 3.3+: CLI parsing
-        $process = new Process(['cmd as array']);
-        if (\is_array($process->getCommandLine())) {
-            // Commandline not parsed, we have Symfony < 3.3
-            return ProcessBuilderFactory::class;
-        }
-
-        return ProcessFactory::class;
-    }
 }
diff --git a/src/Paraunit/Configuration/DependencyInjection/TestResultDefinition.php b/src/Paraunit/Configuration/DependencyInjection/TestResultDefinition.php
index 520a264d..53e83850 100644
--- a/src/Paraunit/Configuration/DependencyInjection/TestResultDefinition.php
+++ b/src/Paraunit/Configuration/DependencyInjection/TestResultDefinition.php
@@ -15,13 +15,13 @@
 
 class TestResultDefinition
 {
-    public function configure(ContainerBuilder $container)
+    public function configure(ContainerBuilder $container): void
     {
         $container->setDefinition(TestResultFactory::class, new Definition(TestResultFactory::class));
         $this->configureTestResultContainer($container);
     }
 
-    private function configureTestResultContainer(ContainerBuilder $container)
+    private function configureTestResultContainer(ContainerBuilder $container): void
     {
         $testResultList = new Definition(TestResultList::class);
 
diff --git a/src/Paraunit/Configuration/PHPUnitConfig.php b/src/Paraunit/Configuration/PHPUnitConfig.php
index 548dbad6..5d0d11f9 100644
--- a/src/Paraunit/Configuration/PHPUnitConfig.php
+++ b/src/Paraunit/Configuration/PHPUnitConfig.php
@@ -39,7 +39,7 @@ public function getBaseDirectory(): string
         return dirname($this->configFilename);
     }
 
-    public function addPhpunitOption(PHPUnitOption $option)
+    public function addPhpunitOption(PHPUnitOption $option): void
     {
         $this->phpunitOptions[] = $option;
     }
diff --git a/src/Paraunit/Configuration/PHPUnitOption.php b/src/Paraunit/Configuration/PHPUnitOption.php
index e0416b50..5368deb1 100644
--- a/src/Paraunit/Configuration/PHPUnitOption.php
+++ b/src/Paraunit/Configuration/PHPUnitOption.php
@@ -33,10 +33,7 @@ public function getName(): string
         return $this->name;
     }
 
-    /**
-     * @return string|null
-     */
-    public function getShortName()
+    public function getShortName(): ?string
     {
         return $this->shortName;
     }
@@ -44,15 +41,12 @@ public function getShortName()
     /**
      * @param string $value
      */
-    public function setValue(string $value = null)
+    public function setValue(string $value = null): void
     {
         $this->value = $value;
     }
 
-    /**
-     * @return string|null
-     */
-    public function getValue()
+    public function getValue(): ?string
     {
         return $this->value;
     }
diff --git a/src/Paraunit/Configuration/ParallelConfiguration.php b/src/Paraunit/Configuration/ParallelConfiguration.php
index 28a990e7..e5b1aeb8 100644
--- a/src/Paraunit/Configuration/ParallelConfiguration.php
+++ b/src/Paraunit/Configuration/ParallelConfiguration.php
@@ -78,7 +78,7 @@ protected function loadCommandLineOptions(ContainerBuilder $containerBuilder, In
         }
     }
 
-    private function enableDebugMode(ContainerBuilder $containerBuilder)
+    private function enableDebugMode(ContainerBuilder $containerBuilder): void
     {
         $definition = new Definition(DebugPrinter::class, [new Reference(OutputInterface::class)]);
         $definition->addTag(self::TAG_EVENT_SUBSCRIBER);
@@ -86,7 +86,7 @@ private function enableDebugMode(ContainerBuilder $containerBuilder)
         $containerBuilder->setDefinition(DebugPrinter::class, $definition);
     }
 
-    private function createPublicAliases(ContainerBuilder $containerBuilder)
+    private function createPublicAliases(ContainerBuilder $containerBuilder): void
     {
         if (! $this->createPublicServiceAliases) {
             return;
@@ -96,11 +96,6 @@ private function createPublicAliases(ContainerBuilder $containerBuilder)
         // the synthetic service isn't listed
         $services[] = OutputInterface::class;
         foreach ($services as $serviceName) {
-            if ($serviceName === 'service_container') {
-                // needed with SF 3.x
-                continue;
-            }
-
             $containerBuilder->setAlias(
                 sprintf(self::PUBLIC_ALIAS_FORMAT, $serviceName),
                 new Alias($serviceName, true)
diff --git a/src/Paraunit/Coverage/CoverageMerger.php b/src/Paraunit/Coverage/CoverageMerger.php
index b57c3fd2..9111fb5f 100644
--- a/src/Paraunit/Coverage/CoverageMerger.php
+++ b/src/Paraunit/Coverage/CoverageMerger.php
@@ -29,7 +29,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function onProcessParsingCompleted(ProcessEvent $processEvent)
+    public function onProcessParsingCompleted(ProcessEvent $processEvent): void
     {
         $process = $processEvent->getProcess();
         if ($process->isToBeRetried()) {
@@ -39,7 +39,7 @@ public function onProcessParsingCompleted(ProcessEvent $processEvent)
         $this->merge($process);
     }
 
-    private function merge(AbstractParaunitProcess $process)
+    private function merge(AbstractParaunitProcess $process): void
     {
         $newCoverageData = $this->coverageFetcher->fetch($process);
 
diff --git a/src/Paraunit/Coverage/CoverageResult.php b/src/Paraunit/Coverage/CoverageResult.php
index 3c4b54f8..7abcab5f 100644
--- a/src/Paraunit/Coverage/CoverageResult.php
+++ b/src/Paraunit/Coverage/CoverageResult.php
@@ -29,12 +29,12 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function addCoverageProcessor(CoverageProcessorInterface $processor)
+    public function addCoverageProcessor(CoverageProcessorInterface $processor): void
     {
         $this->coverageProcessors[] = $processor;
     }
 
-    public function generateResults()
+    public function generateResults(): void
     {
         $coverageData = $this->coverageMerger->getCoverageData();
 
diff --git a/src/Paraunit/Coverage/Processor/AbstractText.php b/src/Paraunit/Coverage/Processor/AbstractText.php
index dd0ea3f7..5cfa32aa 100644
--- a/src/Paraunit/Coverage/Processor/AbstractText.php
+++ b/src/Paraunit/Coverage/Processor/AbstractText.php
@@ -34,7 +34,7 @@ public function __construct(OutputInterface $output, bool $showColors, bool $onl
     /**
      * @throws \RuntimeException
      */
-    public function process(CodeCoverage $coverage)
+    public function process(CodeCoverage $coverage): void
     {
         $coverageResults = $this->text->process($coverage, $this->showColors);
 
diff --git a/src/Paraunit/Coverage/Processor/Clover.php b/src/Paraunit/Coverage/Processor/Clover.php
index 18cc0b50..aa0906b9 100644
--- a/src/Paraunit/Coverage/Processor/Clover.php
+++ b/src/Paraunit/Coverage/Processor/Clover.php
@@ -25,7 +25,7 @@ public function __construct(OutputFile $targetFile)
     /**
      * @throws \RuntimeException
      */
-    public function process(CodeCoverage $codeCoverage)
+    public function process(CodeCoverage $codeCoverage): void
     {
         $this->clover->process($codeCoverage, $this->targetFile->getFilePath());
     }
diff --git a/src/Paraunit/Coverage/Processor/CoverageProcessorInterface.php b/src/Paraunit/Coverage/Processor/CoverageProcessorInterface.php
index 6408f63a..7c50c3d4 100644
--- a/src/Paraunit/Coverage/Processor/CoverageProcessorInterface.php
+++ b/src/Paraunit/Coverage/Processor/CoverageProcessorInterface.php
@@ -10,10 +10,8 @@ interface CoverageProcessorInterface
 {
     /**
      * @throws \RuntimeException If the processor is missing a needed info, like the target dir/filename
-     *
-     * @return void
      */
-    public function process(CodeCoverage $codeCoverage);
+    public function process(CodeCoverage $codeCoverage): void;
 
     public static function getConsoleOptionName(): string;
 }
diff --git a/src/Paraunit/Coverage/Processor/Crap4j.php b/src/Paraunit/Coverage/Processor/Crap4j.php
index 38190f19..acd8bb2b 100644
--- a/src/Paraunit/Coverage/Processor/Crap4j.php
+++ b/src/Paraunit/Coverage/Processor/Crap4j.php
@@ -25,7 +25,7 @@ public function __construct(OutputFile $targetFile)
     /**
      * @throws \RuntimeException
      */
-    public function process(CodeCoverage $codeCoverage)
+    public function process(CodeCoverage $codeCoverage): void
     {
         $this->crap4j->process($codeCoverage, $this->targetFile->getFilePath());
     }
diff --git a/src/Paraunit/Coverage/Processor/Html.php b/src/Paraunit/Coverage/Processor/Html.php
index 49ca6d75..acf7c9e7 100644
--- a/src/Paraunit/Coverage/Processor/Html.php
+++ b/src/Paraunit/Coverage/Processor/Html.php
@@ -25,7 +25,7 @@ public function __construct(OutputPath $targetPath)
     /**
      * @throws \RuntimeException
      */
-    public function process(CodeCoverage $codeCoverage)
+    public function process(CodeCoverage $codeCoverage): void
     {
         $this->html->process($codeCoverage, $this->targetPath->getPath());
     }
diff --git a/src/Paraunit/Coverage/Processor/Php.php b/src/Paraunit/Coverage/Processor/Php.php
index 486e4393..267ff036 100644
--- a/src/Paraunit/Coverage/Processor/Php.php
+++ b/src/Paraunit/Coverage/Processor/Php.php
@@ -25,7 +25,7 @@ public function __construct(OutputFile $targetFile)
     /**
      * @throws \RuntimeException
      */
-    public function process(CodeCoverage $codeCoverage)
+    public function process(CodeCoverage $codeCoverage): void
     {
         $this->php->process($codeCoverage, $this->targetFile->getFilePath());
     }
diff --git a/src/Paraunit/Coverage/Processor/Xml.php b/src/Paraunit/Coverage/Processor/Xml.php
index f7a7b741..53735feb 100644
--- a/src/Paraunit/Coverage/Processor/Xml.php
+++ b/src/Paraunit/Coverage/Processor/Xml.php
@@ -26,7 +26,7 @@ public function __construct(OutputPath $targetPath)
     /**
      * @throws \RuntimeException
      */
-    public function process(CodeCoverage $codeCoverage)
+    public function process(CodeCoverage $codeCoverage): void
     {
         $this->xml->process($codeCoverage, $this->targetPath->getPath());
     }
diff --git a/src/Paraunit/File/Cleaner.php b/src/Paraunit/File/Cleaner.php
index 263666f1..22fadcd7 100644
--- a/src/Paraunit/File/Cleaner.php
+++ b/src/Paraunit/File/Cleaner.php
@@ -25,7 +25,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function purgeCurrentTempDir()
+    public function purgeCurrentTempDir(): void
     {
         self::cleanUpDir($this->tempDirectory->getTempDirForThisExecution());
     }
diff --git a/src/Paraunit/File/TempDirectory.php b/src/Paraunit/File/TempDirectory.php
index 0c4ad4d2..cdc5b1da 100644
--- a/src/Paraunit/File/TempDirectory.php
+++ b/src/Paraunit/File/TempDirectory.php
@@ -62,7 +62,7 @@ public static function getTempBaseDir(): string
     /**
      * @throws \RuntimeException If the dir cannot be created
      */
-    public static function mkdirIfNotExists(string $path)
+    public static function mkdirIfNotExists(string $path): void
     {
         if (file_exists($path)) {
             return;
diff --git a/src/Paraunit/Parser/DeprecationParser.php b/src/Paraunit/Parser/DeprecationParser.php
index 959970e1..85e455e4 100644
--- a/src/Paraunit/Parser/DeprecationParser.php
+++ b/src/Paraunit/Parser/DeprecationParser.php
@@ -27,7 +27,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function handleDeprecations(ProcessEvent $event)
+    public function handleDeprecations(ProcessEvent $event): void
     {
         $process = $event->getProcess();
 
diff --git a/src/Paraunit/Parser/JSON/GenericParser.php b/src/Paraunit/Parser/JSON/GenericParser.php
index 58115eac..ebc96e09 100644
--- a/src/Paraunit/Parser/JSON/GenericParser.php
+++ b/src/Paraunit/Parser/JSON/GenericParser.php
@@ -6,6 +6,7 @@
 
 use Paraunit\Process\AbstractParaunitProcess;
 use Paraunit\TestResult\Interfaces\TestResultHandlerInterface;
+use Paraunit\TestResult\Interfaces\TestResultInterface;
 use Paraunit\TestResult\TestResultFactory;
 
 class GenericParser implements ParserChainElementInterface
@@ -41,7 +42,7 @@ public function __construct(
     /**
      * {@inheritdoc}
      */
-    public function handleLogItem(AbstractParaunitProcess $process, \stdClass $logItem)
+    public function handleLogItem(AbstractParaunitProcess $process, \stdClass $logItem): ?TestResultInterface
     {
         if ($this->logMatches($logItem)) {
             $testResult = $this->testResultFactory->createFromLog($logItem);
diff --git a/src/Paraunit/Parser/JSON/LogParser.php b/src/Paraunit/Parser/JSON/LogParser.php
index b74ee7bd..3d2c065a 100644
--- a/src/Paraunit/Parser/JSON/LogParser.php
+++ b/src/Paraunit/Parser/JSON/LogParser.php
@@ -48,7 +48,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function addParser(ParserChainElementInterface $container)
+    public function addParser(ParserChainElementInterface $container): void
     {
         $this->parsers[] = $container;
     }
@@ -61,7 +61,7 @@ public function getParsers(): array
         return $this->parsers;
     }
 
-    public function onProcessTerminated(ProcessEvent $processEvent)
+    public function onProcessTerminated(ProcessEvent $processEvent): void
     {
         $process = $processEvent->getProcess();
         $logs = $this->logLocator->fetch($process);
@@ -85,7 +85,7 @@ public function onProcessTerminated(ProcessEvent $processEvent)
         $this->eventDispatcher->dispatch(ProcessEvent::PROCESS_PARSING_COMPLETED, new ProcessEvent($process));
     }
 
-    private function processLog(AbstractParaunitProcess $process, \stdClass $logItem)
+    private function processLog(AbstractParaunitProcess $process, \stdClass $logItem): void
     {
         /** @var ParserChainElementInterface $resultContainer */
         foreach ($this->parsers as $resultContainer) {
diff --git a/src/Paraunit/Parser/JSON/LogPrinter.php b/src/Paraunit/Parser/JSON/LogPrinter.php
index 64d081ba..ecf73b06 100644
--- a/src/Paraunit/Parser/JSON/LogPrinter.php
+++ b/src/Paraunit/Parser/JSON/LogPrinter.php
@@ -13,294 +13,287 @@
 use PHPUnit\Framework\TestListener;
 use PHPUnit\Framework\TestSuite;
 use PHPUnit\Framework\Warning;
-use PHPUnit\Runner\Version;
 use PHPUnit\Util;
 
-if (version_compare(Version::id(), '7.0.0', '<')) {
-    class_alias('Paraunit\Parser\JSON\LogPrinterV6', 'Paraunit\Parser\JSON\LogPrinter');
-// Using an early return instead of a else does not work when using the PHPUnit phar due to some weird PHP behavior
-// (the class gets defined without executing the code before it and so the definition is not properly conditional)
-} else {
-    /**
-     * This class comes from Util\Log_JSON.
-     * It's copied and refactored here because it's deprecated in PHPUnit 5.7 and it will be dropped in PHPUnit 6
-     *
-     * Class LogPrinter
-     */
-    class LogPrinter extends Util\Printer implements TestListener
-    {
-        const STATUS_ERROR = 'error';
+/**
+ * This class comes from Util\Log_JSON.
+ * It's copied and refactored here because it's deprecated in PHPUnit 5.7 and it will be dropped in PHPUnit 6
+ *
+ * Class LogPrinter
+ */
+class LogPrinter extends Util\Printer implements TestListener
+{
+    const STATUS_ERROR = 'error';
 
-        const STATUS_WARNING = 'warning';
+    const STATUS_WARNING = 'warning';
 
-        const STATUS_FAIL = 'fail';
+    const STATUS_FAIL = 'fail';
 
-        const STATUS_PASS = 'pass';
+    const STATUS_PASS = 'pass';
 
-        const MESSAGE_INCOMPLETE_TEST = 'Incomplete Test: ';
+    const MESSAGE_INCOMPLETE_TEST = 'Incomplete Test: ';
 
-        const MESSAGE_RISKY_TEST = 'Risky Test: ';
+    const MESSAGE_RISKY_TEST = 'Risky Test: ';
 
-        const MESSAGE_SKIPPED_TEST = 'Skipped Test: ';
+    const MESSAGE_SKIPPED_TEST = 'Skipped Test: ';
 
-        /** @var resource */
-        private $logFile;
+    /** @var resource */
+    private $logFile;
 
-        /** @var string */
-        private $currentTestSuiteName;
+    /** @var string */
+    private $currentTestSuiteName;
 
-        /** @var string */
-        private $currentTestName;
+    /** @var string */
+    private $currentTestName;
 
-        /** @var bool */
-        private $currentTestPass;
+    /** @var bool */
+    private $currentTestPass;
 
-        public function __construct()
-        {
-            $file = fopen($this->getLogFilename(), 'wt');
-            if (! \is_resource($file)) {
-                throw new \RuntimeException('Unable to create log file');
-            }
-            $this->logFile = $file;
-            $this->autoFlush = true;
+    public function __construct()
+    {
+        $file = fopen($this->getLogFilename(), 'wt');
+        if (! \is_resource($file)) {
+            throw new \RuntimeException('Unable to create log file');
         }
+        $this->logFile = $file;
+        $this->autoFlush = true;
+    }
 
-        /**
-         * An error occurred.
-         */
-        public function addError(Test $test, \Throwable $exception, float $time): void
-        {
-            $this->writeCase(
-                self::STATUS_ERROR,
-                $time,
-                $this->getStackTrace($exception),
-                TestFailure::exceptionToString($exception),
-                $test
-            );
-
-            $this->currentTestPass = false;
-        }
+    /**
+     * An error occurred.
+     */
+    public function addError(Test $test, \Throwable $exception, float $time): void
+    {
+        $this->writeCase(
+            self::STATUS_ERROR,
+            $time,
+            $this->getStackTrace($exception),
+            TestFailure::exceptionToString($exception),
+            $test
+        );
+
+        $this->currentTestPass = false;
+    }
 
-        /**
-         * A warning occurred.
-         */
-        public function addWarning(Test $test, Warning $warning, float $time): void
-        {
-            $this->writeCase(
-                self::STATUS_WARNING,
-                $time,
-                $this->getStackTrace($warning),
-                TestFailure::exceptionToString($warning),
-                $test
-            );
-
-            $this->currentTestPass = false;
-        }
+    /**
+     * A warning occurred.
+     */
+    public function addWarning(Test $test, Warning $warning, float $time): void
+    {
+        $this->writeCase(
+            self::STATUS_WARNING,
+            $time,
+            $this->getStackTrace($warning),
+            TestFailure::exceptionToString($warning),
+            $test
+        );
+
+        $this->currentTestPass = false;
+    }
 
-        /**
-         * A failure occurred.
-         */
-        public function addFailure(Test $test, AssertionFailedError $error, float $time): void
-        {
-            $this->writeCase(
-                self::STATUS_FAIL,
-                $time,
-                $this->getStackTrace($error),
-                TestFailure::exceptionToString($error),
-                $test
-            );
-
-            $this->currentTestPass = false;
-        }
+    /**
+     * A failure occurred.
+     */
+    public function addFailure(Test $test, AssertionFailedError $error, float $time): void
+    {
+        $this->writeCase(
+            self::STATUS_FAIL,
+            $time,
+            $this->getStackTrace($error),
+            TestFailure::exceptionToString($error),
+            $test
+        );
+
+        $this->currentTestPass = false;
+    }
 
-        /**
-         * Incomplete test.
-         */
-        public function addIncompleteTest(Test $test, \Throwable $error, float $time): void
-        {
-            $this->writeCase(
-                self::STATUS_ERROR,
-                $time,
-                $this->getStackTrace($error),
-                self::MESSAGE_INCOMPLETE_TEST . $error->getMessage(),
-                $test
-            );
-
-            $this->currentTestPass = false;
-        }
+    /**
+     * Incomplete test.
+     */
+    public function addIncompleteTest(Test $test, \Throwable $error, float $time): void
+    {
+        $this->writeCase(
+            self::STATUS_ERROR,
+            $time,
+            $this->getStackTrace($error),
+            self::MESSAGE_INCOMPLETE_TEST . $error->getMessage(),
+            $test
+        );
+
+        $this->currentTestPass = false;
+    }
 
-        /**
-         * Risky test.
-         */
-        public function addRiskyTest(Test $test, \Throwable $exception, float $time): void
-        {
-            $this->writeCase(
-                self::STATUS_ERROR,
-                $time,
-                $this->getStackTrace($exception),
-                self::MESSAGE_RISKY_TEST . $exception->getMessage(),
-                $test
-            );
-
-            $this->currentTestPass = false;
-        }
+    /**
+     * Risky test.
+     */
+    public function addRiskyTest(Test $test, \Throwable $exception, float $time): void
+    {
+        $this->writeCase(
+            self::STATUS_ERROR,
+            $time,
+            $this->getStackTrace($exception),
+            self::MESSAGE_RISKY_TEST . $exception->getMessage(),
+            $test
+        );
+
+        $this->currentTestPass = false;
+    }
 
-        /**
-         * Skipped test.
-         */
-        public function addSkippedTest(Test $test, \Throwable $exception, float $time): void
-        {
-            $this->writeCase(
-                self::STATUS_ERROR,
-                $time,
-                $this->getStackTrace($exception),
-                self::MESSAGE_SKIPPED_TEST . $exception->getMessage(),
-                $test
-            );
-
-            $this->currentTestPass = false;
-        }
+    /**
+     * Skipped test.
+     */
+    public function addSkippedTest(Test $test, \Throwable $exception, float $time): void
+    {
+        $this->writeCase(
+            self::STATUS_ERROR,
+            $time,
+            $this->getStackTrace($exception),
+            self::MESSAGE_SKIPPED_TEST . $exception->getMessage(),
+            $test
+        );
+
+        $this->currentTestPass = false;
+    }
 
-        /**
-         * A testsuite started.
-         *
-         * @throws \RuntimeException
-         */
-        public function startTestSuite(TestSuite $suite): void
-        {
-            $this->currentTestSuiteName = $suite->getName();
-            $this->currentTestName = '';
-
-            $this->writeArray([
-                'event' => 'suiteStart',
-                'suite' => $this->currentTestSuiteName,
-                'tests' => count($suite),
-            ]);
-        }
+    /**
+     * A testsuite started.
+     *
+     * @throws \RuntimeException
+     */
+    public function startTestSuite(TestSuite $suite): void
+    {
+        $this->currentTestSuiteName = $suite->getName();
+        $this->currentTestName = '';
+
+        $this->writeArray([
+            'event' => 'suiteStart',
+            'suite' => $this->currentTestSuiteName,
+            'tests' => count($suite),
+        ]);
+    }
 
-        public function endTestSuite(TestSuite $suite): void
-        {
-            $this->currentTestSuiteName = '';
-            $this->currentTestName = '';
-        }
+    public function endTestSuite(TestSuite $suite): void
+    {
+        $this->currentTestSuiteName = '';
+        $this->currentTestName = '';
+    }
 
-        public function startTest(Test $test): void
-        {
-            $this->currentTestName = $test instanceof SelfDescribing ? $test->toString() : \get_class($test);
-            $this->currentTestPass = true;
+    public function startTest(Test $test): void
+    {
+        $this->currentTestName = $test instanceof SelfDescribing ? $test->toString() : \get_class($test);
+        $this->currentTestPass = true;
+
+        $this->writeArray([
+            'event' => 'testStart',
+            'suite' => $this->currentTestSuiteName,
+            'test' => $this->currentTestName,
+        ]);
+    }
 
-            $this->writeArray([
-                'event' => 'testStart',
-                'suite' => $this->currentTestSuiteName,
-                'test' => $this->currentTestName,
-            ]);
+    /**
+     * A test ended.
+     */
+    public function endTest(Test $test, float $time): void
+    {
+        if ($this->currentTestPass) {
+            $this->writeCase(self::STATUS_PASS, $time, '', '', $test);
         }
+    }
 
-        /**
-         * A test ended.
-         */
-        public function endTest(Test $test, float $time): void
-        {
-            if ($this->currentTestPass) {
-                $this->writeCase(self::STATUS_PASS, $time, '', '', $test);
-            }
+    /**
+     * @param string $message
+     * @param Test|TestCase|null $test
+     */
+    private function writeCase(string $status, float $time, string $trace, $message = '', $test = null)
+    {
+        $output = '';
+        if ($test instanceof TestCase) {
+            $output = $test->getActualOutput();
         }
 
-        /**
-         * @param string $message
-         * @param Test|TestCase|null $test
-         */
-        private function writeCase(string $status, float $time, string $trace, $message = '', $test = null)
-        {
-            $output = '';
-            if ($test instanceof TestCase) {
-                $output = $test->getActualOutput();
+        $this->writeArray([
+            'event' => 'test',
+            'suite' => $this->currentTestSuiteName,
+            'test' => $this->currentTestName,
+            'status' => $status,
+            'time' => $time,
+            'trace' => $trace,
+            'message' => $this->convertToUtf8($message),
+            'output' => $output,
+        ]);
+    }
+
+    /**
+     * @param array $buffer
+     */
+    private function writeArray($buffer)
+    {
+        array_walk_recursive($buffer, function (&$input) {
+            if (is_string($input)) {
+                $input = $this->convertToUtf8($input);
             }
+        });
 
-            $this->writeArray([
-                'event' => 'test',
-                'suite' => $this->currentTestSuiteName,
-                'test' => $this->currentTestName,
-                'status' => $status,
-                'time' => $time,
-                'trace' => $trace,
-                'message' => $this->convertToUtf8($message),
-                'output' => $output,
-            ]);
-        }
+        $this->writeToLog(json_encode($buffer, JSON_PRETTY_PRINT));
+    }
 
-        /**
-         * @param array $buffer
-         */
-        private function writeArray($buffer)
-        {
-            array_walk_recursive($buffer, function (&$input) {
-                if (is_string($input)) {
-                    $input = $this->convertToUtf8($input);
-                }
-            });
-
-            $this->writeToLog(json_encode($buffer, JSON_PRETTY_PRINT));
+    private function writeToLog($buffer)
+    {
+        // ignore everything that is not a JSON object
+        if ($buffer != '' && $buffer[0] === '{') {
+            \fwrite($this->logFile, $buffer);
+            \fflush($this->logFile);
         }
+    }
 
-        private function writeToLog($buffer)
-        {
-            // ignore everything that is not a JSON object
-            if ($buffer != '' && $buffer[0] === '{') {
-                \fwrite($this->logFile, $buffer);
-                \fflush($this->logFile);
-            }
+    /**
+     * @throws \RuntimeException
+     * @throws \InvalidArgumentException
+     */
+    private function getLogFilename(): string
+    {
+        $logDir = $this->getLogDirectory();
+        if (! @mkdir($logDir, 0777, true) && ! is_dir($logDir)) {
+            throw new \RuntimeException('Cannot create folder for JSON logs');
         }
 
-        /**
-         * @throws \RuntimeException
-         * @throws \InvalidArgumentException
-         */
-        private function getLogFilename(): string
-        {
-            $logDir = $this->getLogDirectory();
-            if (! @mkdir($logDir, 0777, true) && ! is_dir($logDir)) {
-                throw new \RuntimeException('Cannot create folder for JSON logs');
-            }
-
-            $logFilename = getenv(EnvVariables::PROCESS_UNIQUE_ID);
-            if ($logFilename === false) {
-                throw new \InvalidArgumentException('Log filename not received: environment variable not set');
-            }
-
-            return $logDir . $logFilename . '.json.log';
+        $logFilename = getenv(EnvVariables::PROCESS_UNIQUE_ID);
+        if ($logFilename === false) {
+            throw new \InvalidArgumentException('Log filename not received: environment variable not set');
         }
 
-        /**
-         * @throws \InvalidArgumentException
-         */
-        private function getLogDirectory(): string
-        {
-            $logDirectory = getenv(EnvVariables::LOG_DIR);
+        return $logDir . $logFilename . '.json.log';
+    }
 
-            if ($logDirectory === false) {
-                throw new \InvalidArgumentException('Log directory not received: environment variable not set');
-            }
+    /**
+     * @throws \InvalidArgumentException
+     */
+    private function getLogDirectory(): string
+    {
+        $logDirectory = getenv(EnvVariables::LOG_DIR);
 
-            if (substr($logDirectory, -1) !== DIRECTORY_SEPARATOR) {
-                $logDirectory .= DIRECTORY_SEPARATOR;
-            }
+        if ($logDirectory === false) {
+            throw new \InvalidArgumentException('Log directory not received: environment variable not set');
+        }
 
-            return $logDirectory;
+        if (substr($logDirectory, -1) !== DIRECTORY_SEPARATOR) {
+            $logDirectory .= DIRECTORY_SEPARATOR;
         }
 
-        private function convertToUtf8($string): string
-        {
-            if (! \mb_detect_encoding($string, 'UTF-8', true)) {
-                return \mb_convert_encoding($string, 'UTF-8');
-            }
+        return $logDirectory;
+    }
 
-            return $string;
+    private function convertToUtf8($string): string
+    {
+        if (! \mb_detect_encoding($string, 'UTF-8', true)) {
+            return \mb_convert_encoding($string, 'UTF-8');
         }
 
-        private function getStackTrace($error): string
-        {
-            return Util\Filter::getFilteredStacktrace($error);
-        }
+        return $string;
+    }
+
+    private function getStackTrace($error): string
+    {
+        return Util\Filter::getFilteredStacktrace($error);
     }
 }
diff --git a/src/Paraunit/Parser/JSON/LogPrinterV6.php b/src/Paraunit/Parser/JSON/LogPrinterV6.php
deleted file mode 100644
index e0b667f1..00000000
--- a/src/Paraunit/Parser/JSON/LogPrinterV6.php
+++ /dev/null
@@ -1,303 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Paraunit\Parser\JSON;
-
-use Paraunit\Configuration\EnvVariables;
-use PHPUnit\Framework\AssertionFailedError;
-use PHPUnit\Framework\SelfDescribing;
-use PHPUnit\Framework\Test;
-use PHPUnit\Framework\TestCase;
-use PHPUnit\Framework\TestFailure;
-use PHPUnit\Framework\TestListener;
-use PHPUnit\Framework\TestSuite;
-use PHPUnit\Framework\Warning;
-use PHPUnit\Util;
-
-class LogPrinterV6 extends Util\Printer implements TestListener
-{
-    const STATUS_ERROR = 'error';
-
-    const STATUS_WARNING = 'warning';
-
-    const STATUS_FAIL = 'fail';
-
-    const STATUS_PASS = 'pass';
-
-    const MESSAGE_INCOMPLETE_TEST = 'Incomplete Test: ';
-
-    const MESSAGE_RISKY_TEST = 'Risky Test: ';
-
-    const MESSAGE_SKIPPED_TEST = 'Skipped Test: ';
-
-    /** @var resource */
-    private $logFile;
-
-    /** @var string */
-    private $currentTestSuiteName;
-
-    /** @var string */
-    private $currentTestName;
-
-    /** @var bool */
-    private $currentTestPass;
-
-    public function __construct()
-    {
-        $this->logFile = fopen($this->getLogFilename(), 'wt');
-        $this->autoFlush = true;
-    }
-
-    /**
-     * An error occurred.
-     *
-     * @param float $time
-     */
-    public function addError(Test $test, \Exception $exception, $time)
-    {
-        $this->writeCase(
-            self::STATUS_ERROR,
-            $time,
-            $this->getStackTrace($exception),
-            TestFailure::exceptionToString($exception),
-            $test
-        );
-
-        $this->currentTestPass = false;
-    }
-
-    /**
-     * A warning occurred.
-     *
-     * @param float $time
-     */
-    public function addWarning(Test $test, Warning $warning, $time)
-    {
-        $this->writeCase(
-            self::STATUS_WARNING,
-            $time,
-            $this->getStackTrace($warning),
-            TestFailure::exceptionToString($warning),
-            $test
-        );
-
-        $this->currentTestPass = false;
-    }
-
-    /**
-     * A failure occurred.
-     *
-     * @param float $time
-     */
-    public function addFailure(Test $test, AssertionFailedError $error, $time)
-    {
-        $this->writeCase(
-            self::STATUS_FAIL,
-            $time,
-            $this->getStackTrace($error),
-            TestFailure::exceptionToString($error),
-            $test
-        );
-
-        $this->currentTestPass = false;
-    }
-
-    /**
-     * Incomplete test.
-     *
-     * @param float $time
-     */
-    public function addIncompleteTest(Test $test, \Exception $error, $time)
-    {
-        $this->writeCase(
-            self::STATUS_ERROR,
-            $time,
-            $this->getStackTrace($error),
-            self::MESSAGE_INCOMPLETE_TEST . $error->getMessage(),
-            $test
-        );
-
-        $this->currentTestPass = false;
-    }
-
-    /**
-     * Risky test.
-     *
-     * @param float $time
-     */
-    public function addRiskyTest(Test $test, \Exception $exception, $time)
-    {
-        $this->writeCase(
-            self::STATUS_ERROR,
-            $time,
-            $this->getStackTrace($exception),
-            self::MESSAGE_RISKY_TEST . $exception->getMessage(),
-            $test
-        );
-
-        $this->currentTestPass = false;
-    }
-
-    /**
-     * Skipped test.
-     *
-     * @param float $time
-     */
-    public function addSkippedTest(Test $test, \Exception $exception, $time)
-    {
-        $this->writeCase(
-            self::STATUS_ERROR,
-            $time,
-            $this->getStackTrace($exception),
-            self::MESSAGE_SKIPPED_TEST . $exception->getMessage(),
-            $test
-        );
-
-        $this->currentTestPass = false;
-    }
-
-    /**
-     * A testsuite started.
-     *
-     * @throws \RuntimeException
-     */
-    public function startTestSuite(TestSuite $suite)
-    {
-        $this->currentTestSuiteName = $suite->getName();
-        $this->currentTestName = '';
-
-        $this->writeArray([
-            'event' => 'suiteStart',
-            'suite' => $this->currentTestSuiteName,
-            'tests' => count($suite),
-        ]);
-    }
-
-    public function endTestSuite(TestSuite $suite)
-    {
-        $this->currentTestSuiteName = '';
-        $this->currentTestName = '';
-    }
-
-    public function startTest(Test $test)
-    {
-        $this->currentTestName = $test instanceof SelfDescribing ? $test->toString() : \get_class($test);
-        $this->currentTestPass = true;
-
-        $this->writeArray([
-            'event' => 'testStart',
-            'suite' => $this->currentTestSuiteName,
-            'test' => $this->currentTestName,
-        ]);
-    }
-
-    /**
-     * A test ended.
-     *
-     * @param float $time
-     */
-    public function endTest(Test $test, $time)
-    {
-        if ($this->currentTestPass) {
-            $this->writeCase(self::STATUS_PASS, $time, '', '', $test);
-        }
-    }
-
-    /**
-     * @param string $message
-     * @param Test|TestCase|null $test
-     */
-    private function writeCase(string $status, float $time, string $trace, $message = '', $test = null)
-    {
-        $output = '';
-        if ($test instanceof TestCase) {
-            $output = $test->getActualOutput();
-        }
-
-        $this->writeArray([
-            'event' => 'test',
-            'suite' => $this->currentTestSuiteName,
-            'test' => $this->currentTestName,
-            'status' => $status,
-            'time' => $time,
-            'trace' => $trace,
-            'message' => $this->convertToUtf8($message),
-            'output' => $output,
-        ]);
-    }
-
-    /**
-     * @param array $buffer
-     */
-    private function writeArray($buffer)
-    {
-        array_walk_recursive($buffer, function (&$input) {
-            if (is_string($input)) {
-                $input = $this->convertToUtf8($input);
-            }
-        });
-
-        $this->writeToLog(json_encode($buffer, JSON_PRETTY_PRINT));
-    }
-
-    private function writeToLog($buffer)
-    {
-        // ignore everything that is not a JSON object
-        if ($buffer != '' && $buffer[0] === '{') {
-            \fwrite($this->logFile, $buffer);
-            \fflush($this->logFile);
-        }
-    }
-
-    /**
-     * @throws \RuntimeException
-     * @throws \InvalidArgumentException
-     */
-    private function getLogFilename(): string
-    {
-        $logDir = $this->getLogDirectory();
-        if (! @mkdir($logDir, 0777, true) && ! is_dir($logDir)) {
-            throw new \RuntimeException('Cannot create folder for JSON logs');
-        }
-
-        $logFilename = getenv(EnvVariables::PROCESS_UNIQUE_ID);
-        if ($logFilename === false) {
-            throw new \InvalidArgumentException('Log filename not received: environment variable not set');
-        }
-
-        return $logDir . $logFilename . '.json.log';
-    }
-
-    /**
-     * @throws \InvalidArgumentException
-     */
-    private function getLogDirectory(): string
-    {
-        $logDirectory = getenv(EnvVariables::LOG_DIR);
-
-        if ($logDirectory === false) {
-            throw new \InvalidArgumentException('Log directory not received: environment variable not set');
-        }
-
-        if (substr($logDirectory, -1) !== DIRECTORY_SEPARATOR) {
-            $logDirectory .= DIRECTORY_SEPARATOR;
-        }
-
-        return $logDirectory;
-    }
-
-    private function convertToUtf8($string): string
-    {
-        if (! \mb_detect_encoding($string, 'UTF-8', true)) {
-            return \mb_convert_encoding($string, 'UTF-8');
-        }
-
-        return $string;
-    }
-
-    private function getStackTrace($error): string
-    {
-        return Util\Filter::getFilteredStacktrace($error);
-    }
-}
diff --git a/src/Paraunit/Parser/JSON/ParserChainElementInterface.php b/src/Paraunit/Parser/JSON/ParserChainElementInterface.php
index 01fc0270..dedc3e83 100644
--- a/src/Paraunit/Parser/JSON/ParserChainElementInterface.php
+++ b/src/Paraunit/Parser/JSON/ParserChainElementInterface.php
@@ -12,5 +12,5 @@ interface ParserChainElementInterface
     /**
      * @return null|TestResultInterface Returned when the chain needs to stop
      */
-    public function handleLogItem(AbstractParaunitProcess $process, \stdClass $logItem);
+    public function handleLogItem(AbstractParaunitProcess $process, \stdClass $logItem): ?TestResultInterface;
 }
diff --git a/src/Paraunit/Parser/JSON/TestStartParser.php b/src/Paraunit/Parser/JSON/TestStartParser.php
index 31f03a29..5a10cd72 100644
--- a/src/Paraunit/Parser/JSON/TestStartParser.php
+++ b/src/Paraunit/Parser/JSON/TestStartParser.php
@@ -5,6 +5,7 @@
 namespace Paraunit\Parser\JSON;
 
 use Paraunit\Process\AbstractParaunitProcess;
+use Paraunit\TestResult\Interfaces\TestResultInterface;
 use Paraunit\TestResult\NullTestResult;
 
 class TestStartParser implements ParserChainElementInterface
@@ -17,7 +18,7 @@ class TestStartParser implements ParserChainElementInterface
     /** @var string */
     private $lastFunction;
 
-    public function handleLogItem(AbstractParaunitProcess $process, \stdClass $logItem)
+    public function handleLogItem(AbstractParaunitProcess $process, \stdClass $logItem): ?TestResultInterface
     {
         if (property_exists($logItem, 'status') && $logItem->status === LogFetcher::LOG_ENDING_STATUS) {
             return $this->handleLogTermination($process, $logItem);
diff --git a/src/Paraunit/Printer/AbstractFinalPrinter.php b/src/Paraunit/Printer/AbstractFinalPrinter.php
index 9ea4b956..6c3043b7 100644
--- a/src/Paraunit/Printer/AbstractFinalPrinter.php
+++ b/src/Paraunit/Printer/AbstractFinalPrinter.php
@@ -18,5 +18,5 @@ public function __construct(TestResultList $testResultList, OutputInterface $out
         $this->testResultList = $testResultList;
     }
 
-    abstract public function onEngineEnd();
+    abstract public function onEngineEnd(): void;
 }
diff --git a/src/Paraunit/Printer/AbstractPrinter.php b/src/Paraunit/Printer/AbstractPrinter.php
index 31cd2f24..31c161cc 100644
--- a/src/Paraunit/Printer/AbstractPrinter.php
+++ b/src/Paraunit/Printer/AbstractPrinter.php
@@ -16,10 +16,7 @@ public function __construct(OutputInterface $output)
         $this->output = $output;
     }
 
-    /**
-     * @return OutputInterface
-     */
-    public function getOutput()
+    public function getOutput(): OutputInterface
     {
         return $this->output;
     }
diff --git a/src/Paraunit/Printer/ConsoleFormatter.php b/src/Paraunit/Printer/ConsoleFormatter.php
index 228e75c7..0ed23e99 100644
--- a/src/Paraunit/Printer/ConsoleFormatter.php
+++ b/src/Paraunit/Printer/ConsoleFormatter.php
@@ -17,7 +17,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function onEngineBeforeStart()
+    public function onEngineBeforeStart(): void
     {
         $formatter = $this->getOutput()->getFormatter();
         $formatter->setStyle('ok', $this->createNewStyle('green'));
diff --git a/src/Paraunit/Printer/CoveragePrinter.php b/src/Paraunit/Printer/CoveragePrinter.php
index aef2cb9f..039d4e2f 100644
--- a/src/Paraunit/Printer/CoveragePrinter.php
+++ b/src/Paraunit/Printer/CoveragePrinter.php
@@ -35,7 +35,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function onEngineBeforeStart()
+    public function onEngineBeforeStart(): void
     {
         $this->output->write('Coverage driver in use: ');
 
diff --git a/src/Paraunit/Printer/DebugPrinter.php b/src/Paraunit/Printer/DebugPrinter.php
index 5382502f..8a75eb85 100644
--- a/src/Paraunit/Printer/DebugPrinter.php
+++ b/src/Paraunit/Printer/DebugPrinter.php
@@ -19,7 +19,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function onProcessStarted(ProcessEvent $event)
+    public function onProcessStarted(ProcessEvent $event): void
     {
         $process = $event->getProcess();
 
@@ -28,7 +28,7 @@ public function onProcessStarted(ProcessEvent $event)
         $this->getOutput()->writeln('');
     }
 
-    public function onProcessTerminated(ProcessEvent $event)
+    public function onProcessTerminated(ProcessEvent $event): void
     {
         $process = $event->getProcess();
 
@@ -38,12 +38,12 @@ public function onProcessTerminated(ProcessEvent $event)
         $this->getOutput()->writeln('');
     }
 
-    public function onProcessParsingCompleted()
+    public function onProcessParsingCompleted(): void
     {
         $this->getOutput()->write('PROCESS PARSING COMPLETED -- RESULTS: ');
     }
 
-    public function onProcessToBeRetried(ProcessEvent $event)
+    public function onProcessToBeRetried(ProcessEvent $event): void
     {
         $process = $event->getProcess();
 
diff --git a/src/Paraunit/Printer/FailuresPrinter.php b/src/Paraunit/Printer/FailuresPrinter.php
index 30131a67..e5c4ef57 100644
--- a/src/Paraunit/Printer/FailuresPrinter.php
+++ b/src/Paraunit/Printer/FailuresPrinter.php
@@ -13,14 +13,14 @@
 
 class FailuresPrinter extends AbstractFinalPrinter implements EventSubscriberInterface
 {
-    public static function getSubscribedEvents()
+    public static function getSubscribedEvents(): array
     {
         return [
             EngineEvent::END => ['onEngineEnd', 200],
         ];
     }
 
-    public function onEngineEnd()
+    public function onEngineEnd(): void
     {
         foreach ($this->testResultList->getTestResultContainers() as $parser) {
             if ($parser->getTestResultFormat()->shouldPrintTestOutput()) {
@@ -29,7 +29,7 @@ public function onEngineEnd()
         }
     }
 
-    private function printFailuresOutput(TestResultContainer $testResultContainer)
+    private function printFailuresOutput(TestResultContainer $testResultContainer): void
     {
         if (empty($testResultContainer->getTestResults())) {
             return;
@@ -38,26 +38,27 @@ private function printFailuresOutput(TestResultContainer $testResultContainer)
         $tag = $testResultContainer->getTestResultFormat()->getTag();
         $title = $testResultContainer->getTestResultFormat()->getTitle();
 
-        $this->getOutput()->writeln('');
-        $this->getOutput()->writeln(sprintf('<%s>%s output:</%s>', $tag, ucwords($title), $tag));
+        $output = $this->getOutput();
+        $output->writeln('');
+        $output->writeln(sprintf('<%s>%s output:</%s>', $tag, ucwords($title), $tag));
 
         $i = 1;
         foreach ($testResultContainer->getTestResults() as $testResult) {
-            $this->getOutput()->writeln('');
-            $this->getOutput()->write(sprintf('<%s>%d) ', $tag, $i++));
+            $output->writeln('');
+            $output->write(sprintf('<%s>%d) ', $tag, $i++));
 
             if ($testResult instanceof FunctionNameInterface) {
-                $this->getOutput()->writeln($testResult->getFunctionName());
+                $output->writeln($testResult->getFunctionName());
             }
 
-            $this->getOutput()->write(sprintf('</%s>', $tag));
+            $output->write(sprintf('</%s>', $tag));
 
             if ($testResult instanceof FailureMessageInterface) {
-                $this->getOutput()->writeln($testResult->getFailureMessage());
+                $output->writeln($testResult->getFailureMessage());
             }
 
             if ($testResult instanceof StackTraceInterface) {
-                $this->getOutput()->writeln($testResult->getTrace());
+                $output->writeln($testResult->getTrace());
             }
         }
     }
diff --git a/src/Paraunit/Printer/FilesRecapPrinter.php b/src/Paraunit/Printer/FilesRecapPrinter.php
index 4e152158..1d1e0c99 100644
--- a/src/Paraunit/Printer/FilesRecapPrinter.php
+++ b/src/Paraunit/Printer/FilesRecapPrinter.php
@@ -17,14 +17,14 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function onEngineEnd()
+    public function onEngineEnd(): void
     {
         foreach ($this->testResultList->getTestResultContainers() as $parser) {
             $this->printFileRecap($parser);
         }
     }
 
-    private function printFileRecap(TestResultContainerInterface $testResultContainer)
+    private function printFileRecap(TestResultContainerInterface $testResultContainer): void
     {
         if (! $testResultContainer->getTestResultFormat()->shouldPrintFilesRecap()) {
             return;
diff --git a/src/Paraunit/Printer/FinalPrinter.php b/src/Paraunit/Printer/FinalPrinter.php
index 1c8cdbc8..2ff67213 100644
--- a/src/Paraunit/Printer/FinalPrinter.php
+++ b/src/Paraunit/Printer/FinalPrinter.php
@@ -45,12 +45,12 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function onEngineStart()
+    public function onEngineStart(): void
     {
         $this->stopWatch->start(self::STOPWATCH_NAME);
     }
 
-    public function onEngineEnd()
+    public function onEngineEnd(): void
     {
         $stopEvent = $this->stopWatch->stop(self::STOPWATCH_NAME);
 
@@ -58,24 +58,24 @@ public function onEngineEnd()
         $this->printTestCounters();
     }
 
-    public function onProcessTerminated()
+    public function onProcessTerminated(): void
     {
         ++$this->processCompleted;
     }
 
-    public function onProcessToBeRetried()
+    public function onProcessToBeRetried(): void
     {
         ++$this->processRetried;
     }
 
-    private function printExecutionTime(StopwatchEvent $stopEvent)
+    private function printExecutionTime(StopwatchEvent $stopEvent): void
     {
         $this->getOutput()->writeln('');
         $this->getOutput()->writeln('');
         $this->getOutput()->writeln('Execution time -- ' . gmdate('H:i:s', (int) ($stopEvent->getDuration() / 1000)));
     }
 
-    private function printTestCounters()
+    private function printTestCounters(): void
     {
         $testsCount = 0;
         foreach ($this->testResultList->getTestResultContainers() as $container) {
diff --git a/src/Paraunit/Printer/ProcessPrinter.php b/src/Paraunit/Printer/ProcessPrinter.php
index e29d432a..cfd78bc5 100644
--- a/src/Paraunit/Printer/ProcessPrinter.php
+++ b/src/Paraunit/Printer/ProcessPrinter.php
@@ -48,7 +48,7 @@ public static function getSubscribedEvents(): array
     /**
      * @throws \BadMethodCallException
      */
-    public function onProcessCompleted(ProcessEvent $processEvent)
+    public function onProcessCompleted(ProcessEvent $processEvent): void
     {
         $process = $processEvent->getProcess();
 
@@ -57,7 +57,7 @@ public function onProcessCompleted(ProcessEvent $processEvent)
         }
     }
 
-    public function onEngineEnd()
+    public function onEngineEnd(): void
     {
         while (! $this->isRowFull()) {
             $this->output->write(' ');
@@ -67,7 +67,7 @@ public function onEngineEnd()
         $this->printCounter();
     }
 
-    private function printFormattedWithCounter(PrintableTestResultInterface $testResult)
+    private function printFormattedWithCounter(PrintableTestResultInterface $testResult): void
     {
         if ($this->isRowFull()) {
             $this->printCounter();
@@ -81,7 +81,7 @@ private function printFormattedWithCounter(PrintableTestResultInterface $testRes
         );
     }
 
-    private function printCounter()
+    private function printCounter(): void
     {
         $this->output->writeln(sprintf('%6d', $this->counter));
         $this->singleRowCounter = 0;
diff --git a/src/Paraunit/Printer/SharkPrinter.php b/src/Paraunit/Printer/SharkPrinter.php
index 448d17c8..d6ecedc8 100644
--- a/src/Paraunit/Printer/SharkPrinter.php
+++ b/src/Paraunit/Printer/SharkPrinter.php
@@ -28,7 +28,7 @@ public static function getSubscribedEvents(): array
         ];
     }
 
-    public function onEngineBeforeStart()
+    public function onEngineBeforeStart(): void
     {
         $output = $this->getOutput();
 
diff --git a/src/Paraunit/Printer/SingleResultFormatter.php b/src/Paraunit/Printer/SingleResultFormatter.php
index b9b48453..bbd8e00d 100644
--- a/src/Paraunit/Printer/SingleResultFormatter.php
+++ b/src/Paraunit/Printer/SingleResultFormatter.php
@@ -39,7 +39,7 @@ public function formatSingleResult(PrintableTestResultInterface $singleResult):
         return sprintf('<%s>%s</%s>', $tag, $resultSymbol, $tag);
     }
 
-    private function addToMap(TestResultWithSymbolFormat $format)
+    private function addToMap(TestResultWithSymbolFormat $format): void
     {
         $this->tagMap[$format->getTestResultSymbol()] = $format->getTag();
     }
diff --git a/src/Paraunit/Process/AbstractParaunitProcess.php b/src/Paraunit/Process/AbstractParaunitProcess.php
index 92274a71..cc497b8b 100644
--- a/src/Paraunit/Process/AbstractParaunitProcess.php
+++ b/src/Paraunit/Process/AbstractParaunitProcess.php
@@ -48,10 +48,7 @@ abstract public function isTerminated(): bool;
 
     abstract public function getCommandLine(): string;
 
-    /**
-     * @return int|null
-     */
-    abstract public function getExitCode();
+    abstract public function getExitCode(): ?int;
 
     abstract public function start(int $pipelineNumber);
 
@@ -65,12 +62,12 @@ public function getRetryCount(): int
         return $this->retryCount;
     }
 
-    public function increaseRetryCount()
+    public function increaseRetryCount(): void
     {
         ++$this->retryCount;
     }
 
-    public function markAsToBeRetried()
+    public function markAsToBeRetried(): void
     {
         $this->reset();
         $this->increaseRetryCount();
@@ -82,7 +79,7 @@ public function isToBeRetried(): bool
         return $this->shouldBeRetried;
     }
 
-    public function reset()
+    public function reset(): void
     {
         $this->shouldBeRetried = false;
         $this->testResults = [];
@@ -93,15 +90,12 @@ public function getFilename(): string
         return $this->filename;
     }
 
-    /**
-     * @return string|null
-     */
-    public function getTestClassName()
+    public function getTestClassName(): ?string
     {
         return $this->testClassName;
     }
 
-    public function setTestClassName(string $testClassName)
+    public function setTestClassName(string $testClassName): void
     {
         $this->testClassName = $testClassName;
     }
@@ -114,7 +108,7 @@ public function getTestResults(): array
         return $this->testResults;
     }
 
-    public function addTestResult(PrintableTestResultInterface $testResult)
+    public function addTestResult(PrintableTestResultInterface $testResult): void
     {
         $this->testResults[] = $testResult;
         $this->waitingForTestResult = false;
@@ -130,7 +124,7 @@ public function isWaitingForTestResult(): bool
         return $this->waitingForTestResult;
     }
 
-    public function setWaitingForTestResult(bool $waitingForTestResult)
+    public function setWaitingForTestResult(bool $waitingForTestResult): void
     {
         $this->waitingForTestResult = $waitingForTestResult;
     }
diff --git a/src/Paraunit/Process/ProcessBuilderFactory.php b/src/Paraunit/Process/ProcessBuilderFactory.php
deleted file mode 100644
index f5b7a668..00000000
--- a/src/Paraunit/Process/ProcessBuilderFactory.php
+++ /dev/null
@@ -1,51 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Paraunit\Process;
-
-use Paraunit\Configuration\EnvVariables;
-use Paraunit\Configuration\PHPUnitConfig;
-use Paraunit\Configuration\TempFilenameFactory;
-use Symfony\Component\Process\ProcessBuilder;
-
-class ProcessBuilderFactory implements ProcessFactoryInterface
-{
-    /** @var ProcessBuilder */
-    private $builderPrototype;
-
-    /** @var CommandLine */
-    private $cliCommand;
-
-    public function __construct(
-        CommandLine $cliCommand,
-        PHPUnitConfig $phpunitConfig,
-        TempFilenameFactory $tempFilenameFactory
-    ) {
-        $this->cliCommand = $cliCommand;
-        $this->builderPrototype = new ProcessBuilder();
-
-        $this->builderPrototype->addEnvironmentVariables([
-            EnvVariables::LOG_DIR => $tempFilenameFactory->getPathForLog(),
-        ]);
-
-        foreach ($this->cliCommand->getExecutable() as $item) {
-            $this->builderPrototype->add($item);
-        }
-
-        foreach ($this->cliCommand->getOptions($phpunitConfig) as $option) {
-            $this->builderPrototype->add($option);
-        }
-    }
-
-    public function create(string $testFilePath): AbstractParaunitProcess
-    {
-        $builder = clone $this->builderPrototype;
-        $builder->add($testFilePath);
-        foreach ($this->cliCommand->getSpecificOptions($testFilePath) as $specificOption) {
-            $builder->add($specificOption);
-        }
-
-        return new SymfonyProcessWrapper($builder->getProcess(), $testFilePath);
-    }
-}
diff --git a/src/Paraunit/Process/ProcessFactory.php b/src/Paraunit/Process/ProcessFactory.php
index f45f516e..639cb287 100644
--- a/src/Paraunit/Process/ProcessFactory.php
+++ b/src/Paraunit/Process/ProcessFactory.php
@@ -40,10 +40,7 @@ public function create(string $testFilePath): AbstractParaunitProcess
             $this->environmentVariables
         );
 
-        if (method_exists($process, 'inheritEnvironmentVariables')) {
-            // method added in 3.0
-            $process->inheritEnvironmentVariables();
-        }
+        $process->inheritEnvironmentVariables();
 
         return new SymfonyProcessWrapper($process, $testFilePath);
     }
diff --git a/src/Paraunit/Process/SymfonyProcessWrapper.php b/src/Paraunit/Process/SymfonyProcessWrapper.php
index 00b4577f..98ad3323 100644
--- a/src/Paraunit/Process/SymfonyProcessWrapper.php
+++ b/src/Paraunit/Process/SymfonyProcessWrapper.php
@@ -50,10 +50,8 @@ public function getOutput(): string
 
     /**
      * @throws \Symfony\Component\Process\Exception\RuntimeException
-     *
-     * @return int|null
      */
-    public function getExitCode()
+    public function getExitCode(): ?int
     {
         return $this->process->getExitCode();
     }
diff --git a/src/Paraunit/Proxy/Coverage/FakeDriver.php b/src/Paraunit/Proxy/Coverage/FakeDriver.php
index a86ad7e0..f5ef3a92 100644
--- a/src/Paraunit/Proxy/Coverage/FakeDriver.php
+++ b/src/Paraunit/Proxy/Coverage/FakeDriver.php
@@ -4,33 +4,17 @@
 
 namespace Paraunit\Proxy\Coverage;
 
-use PHPUnit\Runner\Version;
 use SebastianBergmann\CodeCoverage\Driver\Driver;
 
-if (version_compare(Version::id(), '7.0.0', '<')) {
-    class FakeDriver implements Driver
+class FakeDriver implements Driver
+{
+    public function start(bool $determineUnusedAndDead = true): void
     {
-        public function start($determineUnusedAndDead = true)
-        {
-            throw new \RuntimeException('This is a fake implementation, it shouldn\'t be used!');
-        }
-
-        public function stop()
-        {
-            throw new \RuntimeException('This is a fake implementation, it shouldn\'t be used!');
-        }
+        throw new \RuntimeException('This is a fake implementation, it shouldn\'t be used!');
     }
-} else {
-    class FakeDriver implements Driver
-    {
-        public function start(bool $determineUnusedAndDead = true): void
-        {
-            throw new \RuntimeException('This is a fake implementation, it shouldn\'t be used!');
-        }
 
-        public function stop(): array
-        {
-            throw new \RuntimeException('This is a fake implementation, it shouldn\'t be used!');
-        }
+    public function stop(): array
+    {
+        throw new \RuntimeException('This is a fake implementation, it shouldn\'t be used!');
     }
 }
diff --git a/src/Paraunit/Runner/PipelineCollection.php b/src/Paraunit/Runner/PipelineCollection.php
index 27933927..9fe8fbd1 100644
--- a/src/Paraunit/Runner/PipelineCollection.php
+++ b/src/Paraunit/Runner/PipelineCollection.php
@@ -58,7 +58,7 @@ public function isEmpty(): bool
         return true;
     }
 
-    public function triggerProcessTermination()
+    public function triggerProcessTermination(): void
     {
         foreach ($this->pipelines as $pipeline) {
             $pipeline->triggerTermination();
diff --git a/src/Paraunit/Runner/Runner.php b/src/Paraunit/Runner/Runner.php
index 6b88daca..93ad62c5 100644
--- a/src/Paraunit/Runner/Runner.php
+++ b/src/Paraunit/Runner/Runner.php
@@ -76,19 +76,19 @@ public function run(): int
         return $this->exitCode;
     }
 
-    public function onProcessParsingCompleted(ProcessEvent $processEvent)
+    public function onProcessParsingCompleted(ProcessEvent $processEvent): void
     {
         if ($processEvent->getProcess()->getExitCode() !== 0) {
             $this->exitCode = 10;
         }
     }
 
-    public function onProcessToBeRetried(ProcessEvent $processEvent)
+    public function onProcessToBeRetried(ProcessEvent $processEvent): void
     {
         $this->queuedProcesses->enqueue($processEvent->getProcess());
     }
 
-    private function createProcessQueue()
+    private function createProcessQueue(): void
     {
         foreach ($this->filter->filterTestFiles() as $file) {
             $this->queuedProcesses->enqueue(
@@ -97,7 +97,7 @@ private function createProcessQueue()
         }
     }
 
-    public function pushToPipeline()
+    public function pushToPipeline(): void
     {
         while (! $this->queuedProcesses->isEmpty() && $this->pipelineCollection->hasEmptySlots()) {
             $this->pipelineCollection->push($this->queuedProcesses->dequeue());
diff --git a/src/Paraunit/TestResult/Interfaces/PrintableTestResultInterface.php b/src/Paraunit/TestResult/Interfaces/PrintableTestResultInterface.php
index b5012083..d22835e0 100644
--- a/src/Paraunit/TestResult/Interfaces/PrintableTestResultInterface.php
+++ b/src/Paraunit/TestResult/Interfaces/PrintableTestResultInterface.php
@@ -10,5 +10,5 @@ interface PrintableTestResultInterface extends TestResultInterface
 {
     public function getTestResultFormat(): TestResultFormat;
 
-    public function setTestResultFormat(TestResultFormat $testResultFormat);
+    public function setTestResultFormat(TestResultFormat $testResultFormat): void;
 }
diff --git a/src/Paraunit/TestResult/Interfaces/TestResultHandlerInterface.php b/src/Paraunit/TestResult/Interfaces/TestResultHandlerInterface.php
index 90f8d9f5..1163b90c 100644
--- a/src/Paraunit/TestResult/Interfaces/TestResultHandlerInterface.php
+++ b/src/Paraunit/TestResult/Interfaces/TestResultHandlerInterface.php
@@ -8,7 +8,7 @@
 
 interface TestResultHandlerInterface
 {
-    public function handleTestResult(AbstractParaunitProcess $process, TestResultInterface $testResult);
+    public function handleTestResult(AbstractParaunitProcess $process, TestResultInterface $testResult): void;
 
-    public function addProcessToFilenames(AbstractParaunitProcess $process);
+    public function addProcessToFilenames(AbstractParaunitProcess $process): void;
 }
diff --git a/src/Paraunit/TestResult/MuteTestResult.php b/src/Paraunit/TestResult/MuteTestResult.php
index c1a2dfa2..b06a7681 100644
--- a/src/Paraunit/TestResult/MuteTestResult.php
+++ b/src/Paraunit/TestResult/MuteTestResult.php
@@ -16,7 +16,7 @@ public function __construct()
         $this->testResultFormat = new TestResultFormat('null', '');
     }
 
-    public function setTestResultFormat(TestResultFormat $testResultFormat)
+    public function setTestResultFormat(TestResultFormat $testResultFormat): void
     {
         $this->testResultFormat = $testResultFormat;
     }
diff --git a/src/Paraunit/TestResult/TestResultContainer.php b/src/Paraunit/TestResult/TestResultContainer.php
index 3aa52f3d..38475930 100644
--- a/src/Paraunit/TestResult/TestResultContainer.php
+++ b/src/Paraunit/TestResult/TestResultContainer.php
@@ -28,7 +28,7 @@ public function __construct(TestResultFormat $testResultFormat)
         $this->testResults = [];
     }
 
-    public function handleTestResult(AbstractParaunitProcess $process, TestResultInterface $testResult)
+    public function handleTestResult(AbstractParaunitProcess $process, TestResultInterface $testResult): void
     {
         $this->addProcessToFilenames($process);
 
@@ -44,7 +44,7 @@ public function handleTestResult(AbstractParaunitProcess $process, TestResultInt
         }
     }
 
-    public function addProcessToFilenames(AbstractParaunitProcess $process)
+    public function addProcessToFilenames(AbstractParaunitProcess $process): void
     {
         // trick for unique
         $this->filenames[$process->getUniqueId()] = $process->getTestClassName() ?: $process->getFilename();
diff --git a/src/Paraunit/TestResult/TestResultList.php b/src/Paraunit/TestResult/TestResultList.php
index 2c964339..73f5e7f6 100644
--- a/src/Paraunit/TestResult/TestResultList.php
+++ b/src/Paraunit/TestResult/TestResultList.php
@@ -14,7 +14,7 @@ public function __construct()
         $this->testResultContainers = [];
     }
 
-    public function addContainer(TestResultContainer $container)
+    public function addContainer(TestResultContainer $container): void
     {
         $this->testResultContainers[] = $container;
     }
diff --git a/src/Paraunit/TestResult/TestResultWithAbnormalTermination.php b/src/Paraunit/TestResult/TestResultWithAbnormalTermination.php
index 84f6f15f..133a0237 100644
--- a/src/Paraunit/TestResult/TestResultWithAbnormalTermination.php
+++ b/src/Paraunit/TestResult/TestResultWithAbnormalTermination.php
@@ -19,7 +19,7 @@ public function getTestOutput(): string
         return $this->testOutput;
     }
 
-    public function setTestOutput(string $testOutput)
+    public function setTestOutput(string $testOutput): void
     {
         $this->testOutput = $testOutput;
     }
diff --git a/tests/Stub/StubbedParaunitProcess.php b/tests/Stub/StubbedParaunitProcess.php
index e30f5c13..dc97b2d9 100644
--- a/tests/Stub/StubbedParaunitProcess.php
+++ b/tests/Stub/StubbedParaunitProcess.php
@@ -77,7 +77,7 @@ public function start(int $pipeline)
         $this->reset();
     }
 
-    public function getExitCode(): int
+    public function getExitCode(): ?int
     {
         return $this->exitCode;
     }
diff --git a/tests/Unit/Process/ProcessBuilderFactoryTest.php b/tests/Unit/Process/ProcessBuilderFactoryTest.php
deleted file mode 100644
index e4602bfe..00000000
--- a/tests/Unit/Process/ProcessBuilderFactoryTest.php
+++ /dev/null
@@ -1,71 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Tests\Unit\Process;
-
-use Paraunit\Configuration\PHPUnitConfig;
-use Paraunit\Configuration\TempFilenameFactory;
-use Paraunit\Process\AbstractParaunitProcess;
-use Paraunit\Process\CommandLine;
-use Paraunit\Process\ProcessBuilderFactory;
-use Tests\BaseUnitTestCase;
-
-class ProcessBuilderFactoryTest extends BaseUnitTestCase
-{
-    protected function setup(): void
-    {
-        if (! \class_exists('Symfony\Component\Process\ProcessBuilder')) {
-            $this->markTestSkipped('This test is legacy, will not work under Symfony 4');
-        }
-
-        parent::setUp(); // TODO: Change the autogenerated stub
-    }
-
-    /**
-     * @group legacy
-     * @expectedDeprecation The Symfony\Component\Process\ProcessBuilder class is deprecated since version 3.4 and will be removed in 4.0. Use the Process class instead
-     */
-    public function testCreateProcess()
-    {
-        $phpUnitConfig = $this->prophesize(PHPUnitConfig::class);
-        $cliCommand = $this->prophesize(CommandLine::class);
-        $cliCommand->getExecutable()->willReturn(['sapi', 'executable']);
-        $cliCommand
-            ->getOptions($phpUnitConfig->reveal())
-            ->shouldBeCalled()
-            ->willReturn(['--configuration=config.xml']);
-        $cliCommand
-            ->getSpecificOptions('TestTest.php')
-            ->shouldBeCalled()
-            ->willReturn(['--specific=value-for-TestTest.php']);
-        $cliCommand
-            ->getSpecificOptions('TestTest2.php')
-            ->shouldBeCalled()
-            ->willReturn(['--specific=value-for-TestTest2.php']);
-
-        $tempFilenameFactory = $this->prophesize(TempFilenameFactory::class);
-        $tempFilenameFactory->getPathForLog()
-            ->willReturn('/path/for/log/');
-
-        $factory = new ProcessBuilderFactory(
-            $cliCommand->reveal(),
-            $phpUnitConfig->reveal(),
-            $tempFilenameFactory->reveal()
-        );
-
-        $processBuilder = $factory->create('TestTest.php');
-
-        $this->assertInstanceOf(AbstractParaunitProcess::class, $processBuilder);
-        $commandLine = $processBuilder->getCommandLine();
-        $this->assertContains('TestTest.php', $commandLine);
-        $this->assertContains('--specific=value-for-TestTest.php', $commandLine);
-
-        $processBuilder = $factory->create('TestTest2.php');
-
-        $this->assertInstanceOf(AbstractParaunitProcess::class, $processBuilder);
-        $commandLine = $processBuilder->getCommandLine();
-        $this->assertContains('TestTest2.php', $commandLine);
-        $this->assertContains('--specific=value-for-TestTest2.php', $commandLine);
-    }
-}
diff --git a/tests/Unit/Process/ProcessFactoryTest.php b/tests/Unit/Process/ProcessFactoryTest.php
index 2484afae..f7e0c119 100644
--- a/tests/Unit/Process/ProcessFactoryTest.php
+++ b/tests/Unit/Process/ProcessFactoryTest.php
@@ -9,21 +9,10 @@
 use Paraunit\Process\AbstractParaunitProcess;
 use Paraunit\Process\CommandLine;
 use Paraunit\Process\ProcessFactory;
-use Symfony\Component\Process\Process;
 use Tests\BaseUnitTestCase;
 
 class ProcessFactoryTest extends BaseUnitTestCase
 {
-    protected function setup(): void
-    {
-        $process = new Process(['cmd as array']);
-        if (\is_array($process->getCommandLine())) {
-            $this->markTestSkipped('CommandLine not parsed, we have symfony/process < 3.3');
-        }
-
-        parent::setUp();
-    }
-
     public function testCreateProcess()
     {
         $phpUnitConfig = $this->prophesize(PHPUnitConfig::class);