diff --git a/.gitignore b/.gitignore
index d5e33e7..ad7b1cf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@
 /coveralls-upload.json
 /phpunit.xml
 /vendor/
+.phpunit.result.cache
diff --git a/.travis.yml b/.travis.yml
index d4cffa2..00a4f8c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,30 +6,30 @@ cache:
 
 env:
   global:
-    - COMPOSER_ARGS="--no-interaction"
+    - COMPOSER_ARGS="--no-interaction --ignore-platform-reqs"
     - COVERAGE_DEPS="php-coveralls/php-coveralls"
 
 matrix:
   fast_finish: true
   include:
-    - php: 7.1
+    - php: 7.3
       env:
         - DEPS=lowest
-    - php: 7.1
+    - php: 7.3
       env:
         - DEPS=latest
         - CS_CHECK=true
         - TEST_COVERAGE=true
-    - php: 7.2
+    - php: 7.4
       env:
         - DEPS=lowest
-    - php: 7.2
+    - php: 7.4
       env:
         - DEPS=latest
-    - php: 7.3
+    - php: nightly
       env:
         - DEPS=lowest
-    - php: 7.3
+    - php: nightly
       env:
         - DEPS=latest
 
@@ -37,7 +37,7 @@ before_install:
   - if [[ $TEST_COVERAGE != 'true' ]]; then phpenv config-rm xdebug.ini || return 0 ; fi
 
 install:
-  - travis_retry composer install $COMPOSER_ARGS --ignore-platform-reqs
+  - travis_retry composer install $COMPOSER_ARGS
   - if [[ $DEPS == 'latest' ]]; then travis_retry composer update $COMPOSER_ARGS ; fi
   - if [[ $DEPS == 'lowest' ]]; then travis_retry composer update --prefer-lowest --prefer-stable $COMPOSER_ARGS ; fi
   - if [[ $TEST_COVERAGE == 'true' ]]; then travis_retry composer require --dev $COMPOSER_ARGS $COVERAGE_DEPS ; fi
diff --git a/composer.json b/composer.json
index 4711509..f0d7a05 100644
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
         }
     },
     "require": {
-        "php": "^7.1",
+        "php": "^7.3 || ~8.0.0",
         "laminas/laminas-zendframework-bridge": "^1.0",
         "mezzio/mezzio-router": "^3.0",
         "psr/container": "^1.0",
@@ -38,9 +38,10 @@
     "require-dev": {
         "laminas/laminas-coding-standard": "~1.0.0",
         "laminas/laminas-diactoros": "^1.7.1",
-        "malukenho/docheader": "^0.1.6",
-        "mockery/mockery": "^1.0",
-        "phpunit/phpunit": "^7.0.2"
+        "malukenho/docheader": "^0.1.8",
+        "mockery/mockery": "^1.4.2",
+        "phpspec/prophecy-phpunit": "^2.0",
+        "phpunit/phpunit": "^9.4.2"
     },
     "autoload": {
         "psr-4": {
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 020be81..4fcfeb2 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,17 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
-         bootstrap="vendor/autoload.php"
-         colors="true">
-    <testsuites>
-        <testsuite name="mezzio-helpers">
-            <directory>./test</directory>
-        </testsuite>
-    </testsuites>
-
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">src</directory>
-        </whitelist>
-    </filter>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd" bootstrap="vendor/autoload.php" colors="true">
+  <coverage processUncoveredFiles="true">
+    <include>
+      <directory suffix=".php">src</directory>
+    </include>
+  </coverage>
+  <testsuites>
+    <testsuite name="mezzio-helpers">
+      <directory>./test</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>
diff --git a/test/BodyParams/BodyParamsMiddlewareTest.php b/test/BodyParams/BodyParamsMiddlewareTest.php
index 2b0d1c4..4687f4c 100644
--- a/test/BodyParams/BodyParamsMiddlewareTest.php
+++ b/test/BodyParams/BodyParamsMiddlewareTest.php
@@ -18,9 +18,11 @@
 use Mezzio\Helper\Exception\MalformedRequestBodyException;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Server\RequestHandlerInterface;
 
+use ReflectionProperty;
 use function fopen;
 use function fwrite;
 use function get_class;
@@ -28,6 +30,8 @@
 
 class BodyParamsMiddlewareTest extends TestCase
 {
+    use ProphecyTrait;
+
     /**
      * @var Stream
      */
@@ -38,7 +42,7 @@ class BodyParamsMiddlewareTest extends TestCase
      */
     private $bodyParams;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->bodyParams = new BodyParamsMiddleware();
 
@@ -275,4 +279,18 @@ public function testParsesJsonBodyWhenExpected($method)
         $this->assertInstanceOf(Response::class, $result);
         $this->assertTrue($handlerTriggered);
     }
+
+    private function assertAttributeSame($expected, $attribute, $object)
+    {
+        $r = new ReflectionProperty($object, $attribute);
+        $r->setAccessible(true);
+        self::assertSame($expected, $r->getValue($object));
+    }
+
+    private function assertAttributeContains($expected, $attribute, $object)
+    {
+        $r = new ReflectionProperty($object, $attribute);
+        $r->setAccessible(true);
+        self::assertContains($expected, $r->getValue($object));
+    }
 }
diff --git a/test/BodyParams/FormUrlEncodedStrategyTest.php b/test/BodyParams/FormUrlEncodedStrategyTest.php
index 57a6e2b..699f869 100644
--- a/test/BodyParams/FormUrlEncodedStrategyTest.php
+++ b/test/BodyParams/FormUrlEncodedStrategyTest.php
@@ -12,17 +12,20 @@
 
 use Mezzio\Helper\BodyParams\FormUrlEncodedStrategy;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Message\StreamInterface;
 
 class FormUrlEncodedStrategyTest extends TestCase
 {
+    use ProphecyTrait;
+
     /**
      * @var FormUrlEncodedStrategy
      */
     private $strategy;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->strategy = new FormUrlEncodedStrategy();
     }
diff --git a/test/BodyParams/JsonStrategyTest.php b/test/BodyParams/JsonStrategyTest.php
index 232d4be..7af96dd 100644
--- a/test/BodyParams/JsonStrategyTest.php
+++ b/test/BodyParams/JsonStrategyTest.php
@@ -13,17 +13,20 @@
 use Mezzio\Helper\BodyParams\JsonStrategy;
 use Mezzio\Helper\Exception\MalformedRequestBodyException;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Message\StreamInterface;
 
 class JsonStrategyTest extends TestCase
 {
+    use ProphecyTrait;
+
     /**
      * @var JsonStrategy
      */
     private $strategy;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->strategy = new JsonStrategy();
     }
diff --git a/test/ConfigProviderTest.php b/test/ConfigProviderTest.php
index 2e42e59..ca64287 100644
--- a/test/ConfigProviderTest.php
+++ b/test/ConfigProviderTest.php
@@ -32,7 +32,7 @@ protected function setUp() : void
     public function testInvocationReturnsArray() : array
     {
         $config = ($this->provider)();
-        $this->assertInternalType('array', $config);
+        $this->assertIsArray($config);
 
         return $config;
     }
@@ -43,14 +43,14 @@ public function testInvocationReturnsArray() : array
     public function testReturnedArrayContainsDependencies(array $config) : void
     {
         $this->assertArrayHasKey('dependencies', $config);
-        $this->assertInternalType('array', $config['dependencies']);
+        $this->assertIsArray($config['dependencies']);
 
         $this->assertArrayHasKey('invokables', $config['dependencies']);
-        $this->assertInternalType('array', $config['dependencies']['invokables']);
+        $this->assertIsArray($config['dependencies']['invokables']);
         $this->assertArrayHasKey(ServerUrlHelper::class, $config['dependencies']['invokables']);
 
         $this->assertArrayHasKey('factories', $config['dependencies']);
-        $this->assertInternalType('array', $config['dependencies']['factories']);
+        $this->assertIsArray($config['dependencies']['factories']);
         $this->assertArrayHasKey(ServerUrlMiddleware::class, $config['dependencies']['factories']);
         $this->assertArrayHasKey(UrlHelper::class, $config['dependencies']['factories']);
         $this->assertArrayHasKey(UrlHelperMiddleware::class, $config['dependencies']['factories']);
diff --git a/test/ContentLengthMiddlewareTest.php b/test/ContentLengthMiddlewareTest.php
index effe0bb..b878d25 100644
--- a/test/ContentLengthMiddlewareTest.php
+++ b/test/ContentLengthMiddlewareTest.php
@@ -12,6 +12,7 @@
 
 use Mezzio\Helper\ContentLengthMiddleware;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Message\StreamInterface;
@@ -19,7 +20,9 @@
 
 class ContentLengthMiddlewareTest extends TestCase
 {
-    public function setUp()
+    use ProphecyTrait;
+
+    public function setUp(): void
     {
         $this->response = $response = $this->prophesize(ResponseInterface::class);
         $this->request = $request = $this->prophesize(ServerRequestInterface::class)->reveal();
diff --git a/test/ExceptionTest.php b/test/ExceptionTest.php
index 16ca93f..b0c1c9a 100644
--- a/test/ExceptionTest.php
+++ b/test/ExceptionTest.php
@@ -39,7 +39,7 @@ public function exception() : Generator
      */
     public function testExceptionIsInstanceOfExceptionInterface(string $exception) : void
     {
-        self::assertContains('Exception', $exception);
+        self::assertStringContainsString('Exception', $exception);
         self::assertTrue(is_a($exception, ExceptionInterface::class, true));
     }
 }
diff --git a/test/ServerUrlMiddlewareFactoryTest.php b/test/ServerUrlMiddlewareFactoryTest.php
index 5ba6a80..7747689 100644
--- a/test/ServerUrlMiddlewareFactoryTest.php
+++ b/test/ServerUrlMiddlewareFactoryTest.php
@@ -15,10 +15,13 @@
 use Mezzio\Helper\ServerUrlMiddleware;
 use Mezzio\Helper\ServerUrlMiddlewareFactory;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Container\ContainerInterface;
 
 class ServerUrlMiddlewareFactoryTest extends TestCase
 {
+    use ProphecyTrait;
+
     public function testCreatesAndReturnsMiddlewareWhenHelperIsPresentInContainer()
     {
         $helper = $this->prophesize(ServerUrlHelper::class);
diff --git a/test/ServerUrlMiddlewareTest.php b/test/ServerUrlMiddlewareTest.php
index e481b77..9f2ca44 100644
--- a/test/ServerUrlMiddlewareTest.php
+++ b/test/ServerUrlMiddlewareTest.php
@@ -15,13 +15,17 @@
 use Mezzio\Helper\ServerUrlMiddleware;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Message\UriInterface;
 use Psr\Http\Server\RequestHandlerInterface;
+use ReflectionProperty;
 
 class ServerUrlMiddlewareTest extends TestCase
 {
+    use ProphecyTrait;
+
     public function testMiddlewareInjectsHelperWithUri()
     {
         $uri = $this->prophesize(UriInterface::class);
@@ -44,11 +48,8 @@ public function testMiddlewareInjectsHelperWithUri()
         //$this->assertSame($response->reveal(), $test, 'Unexpected return value from middleware');
         $this->assertTrue($invoked, 'next() was not invoked');
 
-        $this->assertAttributeSame(
-            $uri->reveal(),
-            'uri',
-            $helper,
-            'Helper was not injected with URI from request'
-        );
+        $r = new ReflectionProperty($helper, 'uri');
+        $r->setAccessible(true);
+        self::assertSame($uri->reveal(), $r->getValue($helper), 'Helper was not injected with URI from request');
     }
 }
diff --git a/test/Template/RouteTemplateVariableMiddlewareTest.php b/test/Template/RouteTemplateVariableMiddlewareTest.php
index 736aeb6..9374fbf 100644
--- a/test/Template/RouteTemplateVariableMiddlewareTest.php
+++ b/test/Template/RouteTemplateVariableMiddlewareTest.php
@@ -16,6 +16,7 @@
 use Mezzio\Router\RouteResult;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Server\MiddlewareInterface;
@@ -23,7 +24,9 @@
 
 class RouteTemplateVariableMiddlewareTest extends TestCase
 {
-    public function setUp()
+    use ProphecyTrait;
+
+    public function setUp(): void
     {
         $this->request    = $this->prophesize(ServerRequestInterface::class);
         $this->response   = $this->prophesize(ResponseInterface::class);
diff --git a/test/Template/TemplateVariableContainerMiddlewareTest.php b/test/Template/TemplateVariableContainerMiddlewareTest.php
index fb59467..bab79ed 100644
--- a/test/Template/TemplateVariableContainerMiddlewareTest.php
+++ b/test/Template/TemplateVariableContainerMiddlewareTest.php
@@ -14,13 +14,16 @@
 use Mezzio\Helper\Template\TemplateVariableContainerMiddleware;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Server\RequestHandlerInterface;
 
 class TemplateVariableContainerMiddlewareTest extends TestCase
 {
-    public function setUp()
+    use ProphecyTrait;
+
+    public function setUp(): void
     {
         $this->handler    = $this->prophesize(RequestHandlerInterface::class);
         $this->request    = $this->prophesize(ServerRequestInterface::class);
diff --git a/test/Template/TemplateVariableContainerTest.php b/test/Template/TemplateVariableContainerTest.php
index 97428e5..60c77e3 100644
--- a/test/Template/TemplateVariableContainerTest.php
+++ b/test/Template/TemplateVariableContainerTest.php
@@ -15,7 +15,7 @@
 
 class TemplateVariableContainerTest extends TestCase
 {
-    public function setUp()
+    public function setUp(): void
     {
         $this->container = new TemplateVariableContainer();
     }
diff --git a/test/UrlHelperFactoryTest.php b/test/UrlHelperFactoryTest.php
index c65318f..38655f5 100644
--- a/test/UrlHelperFactoryTest.php
+++ b/test/UrlHelperFactoryTest.php
@@ -15,11 +15,15 @@
 use Mezzio\Helper\UrlHelperFactory;
 use Mezzio\Router\RouterInterface;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Prophecy\Prophecy\ObjectProphecy;
 use Psr\Container\ContainerInterface;
+use ReflectionProperty;
 
 class UrlHelperFactoryTest extends TestCase
 {
+    use ProphecyTrait;
+
     /**
      * @var RouterInterface|ObjectProphecy
      */
@@ -35,7 +39,7 @@ class UrlHelperFactoryTest extends TestCase
      */
     private $factory;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->router = $this->prophesize(RouterInterface::class);
         $this->container = $this->prophesize(ContainerInterface::class);
@@ -96,4 +100,11 @@ public function testFactoryAllowsSerialization()
         $this->assertAttributeSame('/api', 'basePath', $factory);
         $this->assertAttributeSame(Router::class, 'routerServiceName', $factory);
     }
+
+    private function assertAttributeSame($expected, $attribute, $object)
+    {
+        $r = new ReflectionProperty($object, $attribute);
+        $r->setAccessible(true);
+        self::assertSame($expected, $r->getValue($object));
+    }
 }
diff --git a/test/UrlHelperMiddlewareFactoryTest.php b/test/UrlHelperMiddlewareFactoryTest.php
index 7d805db..ebcfec0 100644
--- a/test/UrlHelperMiddlewareFactoryTest.php
+++ b/test/UrlHelperMiddlewareFactoryTest.php
@@ -15,17 +15,21 @@
 use Mezzio\Helper\UrlHelperMiddleware;
 use Mezzio\Helper\UrlHelperMiddlewareFactory;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Prophecy\Prophecy\ObjectProphecy;
 use Psr\Container\ContainerInterface;
+use ReflectionProperty;
 
 class UrlHelperMiddlewareFactoryTest extends TestCase
 {
+    use ProphecyTrait;
+
     /**
      * @var ContainerInterface|ObjectProphecy
      */
     private $container;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->container = $this->prophesize(ContainerInterface::class);
     }
@@ -78,4 +82,11 @@ public function testFactoryAllowsSerialization()
         $this->assertInstanceOf(UrlHelperMiddlewareFactory::class, $factory);
         $this->assertAttributeSame(MyUrlHelper::class, 'urlHelperServiceName', $factory);
     }
+
+    private function assertAttributeSame($expected, $attribute, $object)
+    {
+        $r = new ReflectionProperty($object, $attribute);
+        $r->setAccessible(true);
+        self::assertSame($expected, $r->getValue($object));
+    }
 }
diff --git a/test/UrlHelperMiddlewareTest.php b/test/UrlHelperMiddlewareTest.php
index 3a0ff34..3d2f5d1 100644
--- a/test/UrlHelperMiddlewareTest.php
+++ b/test/UrlHelperMiddlewareTest.php
@@ -15,6 +15,7 @@
 use Mezzio\Router\RouteResult;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Prophecy\Prophecy\ObjectProphecy;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
@@ -22,12 +23,14 @@
 
 class UrlHelperMiddlewareTest extends TestCase
 {
+    use ProphecyTrait;
+
     /**
      * @var UrlHelper|ObjectProphecy
      */
     private $helper;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->helper = $this->prophesize(UrlHelper::class);
     }
diff --git a/test/UrlHelperTest.php b/test/UrlHelperTest.php
index 9a9ae42..7b82107 100644
--- a/test/UrlHelperTest.php
+++ b/test/UrlHelperTest.php
@@ -19,12 +19,16 @@
 use Mockery;
 use Mockery\Adapter\Phpunit\MockeryPHPUnitIntegration;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Prophecy\Prophecy\ObjectProphecy;
+use ReflectionProperty;
 use stdClass;
 use TypeError;
 
 class UrlHelperTest extends TestCase
 {
+    use ProphecyTrait;
+
     use MockeryPHPUnitIntegration;
 
     /**
@@ -32,7 +36,7 @@ class UrlHelperTest extends TestCase
      */
     private $router;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->router = $this->prophesize(RouterInterface::class);
     }
@@ -393,4 +397,18 @@ public function testGetRouteResultWithRouteResultSet()
         $helper->setRouteResult($result->reveal());
         $this->assertInstanceOf(RouteResult::class, $helper->getRouteResult());
     }
+
+    private function assertAttributeSame($expected, $attribute, $object)
+    {
+        $r = new ReflectionProperty($object, $attribute);
+        $r->setAccessible(true);
+        self::assertSame($expected, $r->getValue($object));
+    }
+
+    private function assertAttributeEquals($expected, $attribute, $object)
+    {
+        $r = new ReflectionProperty($object, $attribute);
+        $r->setAccessible(true);
+        self::assertEquals($expected, $r->getValue($object));
+    }
 }