diff --git a/.github/workflows/php.yml b/.github/workflows/php.yml
index b85b2e4..729dc39 100644
--- a/.github/workflows/php.yml
+++ b/.github/workflows/php.yml
@@ -8,10 +8,10 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-versions: ['7.3', '7.4', '8.0', '8.1']
+        php-versions: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
     steps:
     - name: Checkout
       uses: actions/checkout@v2
diff --git a/.gitignore b/.gitignore
index 16ab1dc..c328a78 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 composer.lock
 phpunit.xml
 phpcs.xml
+.*
diff --git a/composer.json b/composer.json
index 282658f..84490f6 100644
--- a/composer.json
+++ b/composer.json
@@ -7,11 +7,11 @@
         "sort-packages": true
     },
     "require": {
-        "php": "^7.3 || ^8.0",
+        "php": "^7.0||^8.0",
         "psr/simple-cache": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.3",
+        "phpunit/phpunit": ">=6.5",
         "squizlabs/php_codesniffer": "^3.3"
     },
     "autoload": {
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index b2616af..be8e64f 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,17 +1,13 @@
 <?xml version="1.0"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" colors="true" forceCoversAnnotation="true" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
-  <coverage>
-    <include>
-      <directory>src</directory>
-    </include>
-    <report>
-      <clover outputFile="./clover.xml"/>
-    </report>
-  </coverage>
   <testsuites>
     <testsuite name="PHP Library Test Suite">
       <directory suffix="Test.php">tests</directory>
     </testsuite>
   </testsuites>
-  <logging/>
+  <filter>
+    <whitelist>
+        <directory>src</directory>
+    </whitelist>
+  </filter>
 </phpunit>
diff --git a/tests/InMemoryCacheTest.php b/tests/InMemoryCacheTest.php
index fac178c..46077ef 100644
--- a/tests/InMemoryCacheTest.php
+++ b/tests/InMemoryCacheTest.php
@@ -13,25 +13,6 @@
  */
 final class InMemoryCacheTest extends \PHPUnit\Framework\TestCase
 {
-    /**
-     * @var InMemoryCache
-     */
-    private $cache;
-
-    /**
-     * @var ArrayObject
-     */
-    private $container;
-
-    /**
-     * @return void
-     */
-    public function setUp() : void
-    {
-        $this->container = new ArrayObject();
-        $this->cache = new InMemoryCache($this->container);
-    }
-
     /**
      * @test
      * @covers ::get
@@ -40,9 +21,11 @@ public function setUp() : void
      */
     public function get()
     {
+        $container = new ArrayObject();
+        $cache = new InMemoryCache($container);
         $dateTime = new DateTime();
-        $this->container['foo'] = ['data' => $dateTime, 'expires' => PHP_INT_MAX];
-        $this->assertEquals($dateTime, $this->cache->get('foo'));
+        $container['foo'] = ['data' => $dateTime, 'expires' => PHP_INT_MAX];
+        $this->assertEquals($dateTime, $cache->get('foo'));
     }
 
     /**
@@ -53,8 +36,9 @@ public function get()
      */
     public function getKeyNotFound()
     {
+        $cache = new InMemoryCache(new ArrayObject());
         $default = new \StdClass();
-        $this->assertSame($default, $this->cache->get('foo', $default));
+        $this->assertSame($default, $cache->get('foo', $default));
     }
 
     /**
@@ -65,8 +49,10 @@ public function getKeyNotFound()
      */
     public function getExpired()
     {
-        $this->container['foo'] = ['data' => new DateTime(), 'expires' => -10];
-        $this->assertNull($this->cache->get('foo'));
+        $container = new ArrayObject();
+        $container['foo'] = ['data' => new DateTime(), 'expires' => -10];
+        $cache = new InMemoryCache($container);
+        $this->assertNull($cache->get('foo'));
     }
 
     /**
@@ -77,12 +63,13 @@ public function getExpired()
      */
     public function getMultple()
     {
+        $cache = new InMemoryCache(new ArrayObject());
         $default = new \StdClass();
         $dateTime = new \DateTime();
         $exception = new \RuntimeException();
-        $this->cache->set('foo', $dateTime);
-        $this->cache->set('bar', $exception);
-        $actual = $this->cache->getMultiple(['foo', 'baz', 'bar'], $default);
+        $cache->set('foo', $dateTime);
+        $cache->set('bar', $exception);
+        $actual = $cache->getMultiple(['foo', 'baz', 'bar'], $default);
         $this->assertEquals($dateTime, $actual['foo']);
         $this->assertSame($default, $actual['baz']);
         $this->assertEquals($exception, $actual['bar']);
@@ -96,8 +83,10 @@ public function getMultple()
      */
     public function setWithIntegerTTL()
     {
+        $container = new ArrayObject();
+        $cache = new InMemoryCache($container);
         $dateTime = new \DateTime();
-        $this->assertTrue($this->cache->set('foo', $dateTime, 3600));
+        $this->assertTrue($cache->set('foo', $dateTime, 3600));
         $this->assertSame(
             [
                 'foo' => [
@@ -105,7 +94,7 @@ public function setWithIntegerTTL()
                     'expires' => time() + 3600,
                 ],
             ],
-            $this->container->getArrayCopy()
+            $container->getArrayCopy()
         );
     }
 
@@ -118,8 +107,9 @@ public function setWithIntegerTTL()
     public function setWithNullTTL()
     {
         $dateTime = new \DateTime();
-        $this->assertTrue($this->cache->set('foo', $dateTime));
-        $this->assertEquals($dateTime, $this->cache->get('foo'));
+        $cache = new InMemoryCache(new ArrayObject());
+        $this->assertTrue($cache->set('foo', $dateTime));
+        $this->assertEquals($dateTime, $cache->get('foo'));
     }
 
     /**
@@ -133,9 +123,10 @@ public function setMultple()
         $ttl = \DateInterval::createFromDateString('1 day');
         $dateTime = new \DateTime();
         $exception = new \RuntimeException();
-        $this->assertTrue($this->cache->setMultiple(['foo' => $dateTime, 'bar' => $exception], $ttl));
-        $this->assertEquals($dateTime, $this->cache->get('foo'));
-        $this->assertEquals($exception, $this->cache->get('bar'));
+        $cache = new InMemoryCache(new ArrayObject());
+        $this->assertTrue($cache->setMultiple(['foo' => $dateTime, 'bar' => $exception], $ttl));
+        $this->assertEquals($dateTime, $cache->get('foo'));
+        $this->assertEquals($exception, $cache->get('bar'));
     }
 
     /**
@@ -146,10 +137,11 @@ public function setMultple()
      */
     public function delete()
     {
+        $cache = new InMemoryCache(new ArrayObject());
         $dateTime = new DateTime();
-        $this->cache->set('foo', $dateTime);
-        $this->cache->delete('foo');
-        $this->assertNull($this->cache->get('foo'));
+        $cache->set('foo', $dateTime);
+        $cache->delete('foo');
+        $this->assertNull($cache->get('foo'));
     }
 
     /**
@@ -160,14 +152,15 @@ public function delete()
      */
     public function deleteMultiple()
     {
-        $this->cache->set('foo', 'foo');
-        $this->cache->set('bar', 'bar');
-        $this->cache->set('baz', 'baz');
-
-        $this->cache->deleteMultiple(['foo', 'bar']);
-        $this->assertNull($this->cache->get('foo'));
-        $this->assertNull($this->cache->get('bar'));
-        $this->assertSame('baz', $this->cache->get('baz'));
+        $cache = new InMemoryCache(new ArrayObject());
+        $cache->set('foo', 'foo');
+        $cache->set('bar', 'bar');
+        $cache->set('baz', 'baz');
+
+        $cache->deleteMultiple(['foo', 'bar']);
+        $this->assertNull($cache->get('foo'));
+        $this->assertNull($cache->get('bar'));
+        $this->assertSame('baz', $cache->get('baz'));
     }
 
     /**
@@ -178,13 +171,15 @@ public function deleteMultiple()
      */
     public function clear()
     {
-        $this->cache->set('foo', 'foo');
-        $this->cache->set('bar', 'bar');
-        $this->cache->set('baz', 'baz');
+        $container = new ArrayObject();
+        $cache = new InMemoryCache($container);
+        $cache->set('foo', 'foo');
+        $cache->set('bar', 'bar');
+        $cache->set('baz', 'baz');
 
-        $this->cache->clear();
+        $cache->clear();
 
-        $this->assertSame([], $this->container->getArrayCopy());
+        $this->assertSame([], $container->getArrayCopy());
     }
 
     /**
@@ -195,8 +190,9 @@ public function clear()
      */
     public function has()
     {
-        $this->cache->set('foo', 'foo');
-        $this->assertTrue($this->cache->has('foo'));
-        $this->assertFalse($this->cache->has('bar'));
+        $cache = new InMemoryCache(new ArrayObject());
+        $cache->set('foo', 'foo');
+        $this->assertTrue($cache->has('foo'));
+        $this->assertFalse($cache->has('bar'));
     }
 }
diff --git a/tests/KeyValidatorTraitTest.php b/tests/KeyValidatorTraitTest.php
index 80ce1ad..8f1dae0 100644
--- a/tests/KeyValidatorTraitTest.php
+++ b/tests/KeyValidatorTraitTest.php
@@ -68,13 +68,13 @@ public function validateKeysWithInvalidValue($key)
      *
      * @return array
      */
-    public function provideInvalidKeys() : array
+    public static function provideInvalidKeys() : array
     {
         return [
-            ['an empty string' => ''],
-            ['an object' => new \StdClass()],
-            ['an integer' => 123],
-            ['reserved characters' => '@key'],
+            [''],
+            [new \StdClass()],
+            [123],
+            ['@key'],
         ];
     }
 }
diff --git a/tests/NullCacheTest.php b/tests/NullCacheTest.php
index bde50b1..fbd9b5d 100644
--- a/tests/NullCacheTest.php
+++ b/tests/NullCacheTest.php
@@ -11,23 +11,6 @@
  */
 final class NullCacheTest extends \PHPUnit\Framework\TestCase
 {
-    /**
-     * NullCache instance to use in tests.
-     *
-     * @var NullCache
-     */
-    private $cache;
-
-    /**
-     * Prepare each test
-     *
-     * @return void
-     */
-    public function setUp() : void
-    {
-        $this->cache = new NullCache();
-    }
-
     /**
      * Verify basic behavior of get().
      *
@@ -38,8 +21,9 @@ public function setUp() : void
      */
     public function get()
     {
+        $cache = new NullCache();
         $default = new \StdClass();
-        $this->assertSame($default, $this->cache->get('a key', $default));
+        $this->assertSame($default, $cache->get('a key', $default));
     }
 
     /**
@@ -52,7 +36,8 @@ public function get()
      */
     public function set()
     {
-        $this->assertTrue($this->cache->set('a key', 'some data'));
+        $cache = new NullCache();
+        $this->assertTrue($cache->set('a key', 'some data'));
     }
 
     /**
@@ -65,7 +50,8 @@ public function set()
      */
     public function delete()
     {
-        $this->assertTrue($this->cache->delete('a key'));
+        $cache = new NullCache();
+        $this->assertTrue($cache->delete('a key'));
     }
 
     /**
@@ -78,7 +64,8 @@ public function delete()
      */
     public function clear()
     {
-        $this->assertTrue($this->cache->clear());
+        $cache = new NullCache();
+        $this->assertTrue($cache->clear());
     }
 
     /**
@@ -91,10 +78,11 @@ public function clear()
      */
     public function getMultiple()
     {
+        $cache = new NullCache();
         $default = new \StdClass();
         $this->assertSame(
             ['key1' => $default, 'key2' => $default],
-            $this->cache->getMultiple(['key1', 'key2'], $default)
+            $cache->getMultiple(['key1', 'key2'], $default)
         );
     }
 
@@ -108,7 +96,8 @@ public function getMultiple()
      */
     public function setMultiple()
     {
-        $this->assertTrue($this->cache->setMultiple(['key' => 'some data', 'key2' => 'some more data']));
+        $cache = new NullCache();
+        $this->assertTrue($cache->setMultiple(['key' => 'some data', 'key2' => 'some more data']));
     }
 
     /**
@@ -121,7 +110,8 @@ public function setMultiple()
      */
     public function deleteMultiple()
     {
-        $this->assertTrue($this->cache->deleteMultiple(['key1', 'key2']));
+        $cache = new NullCache();
+        $this->assertTrue($cache->deleteMultiple(['key1', 'key2']));
     }
 
     /**
@@ -134,6 +124,7 @@ public function deleteMultiple()
      */
     public function has()
     {
-        $this->assertFalse($this->cache->has('key1'));
+        $cache = new NullCache();
+        $this->assertFalse($cache->has('key1'));
     }
 }
diff --git a/tests/Serializer/NullSerializerTest.php b/tests/Serializer/NullSerializerTest.php
index 193e332..f287039 100644
--- a/tests/Serializer/NullSerializerTest.php
+++ b/tests/Serializer/NullSerializerTest.php
@@ -10,21 +10,6 @@
  */
 final class NullSerializerTest extends \PHPUnit\Framework\TestCase
 {
-    /**
-     * @var NullSerializer
-     */
-    private $serializer;
-
-    /**
-     * Prepare each test
-     *
-     * @return void
-     */
-    public function setUp() : void
-    {
-        $this->serializer = new NullSerializer();
-    }
-
     /**
      * @test
      * @covers ::unserialize
@@ -33,8 +18,9 @@ public function setUp() : void
      */
     public function unserialize()
     {
+        $serializer = new NullSerializer();
         $data = ['foo' => 'abc', 'bar' => 123];
-        $this->assertSame($data, $this->serializer->unserialize($data));
+        $this->assertSame($data, $serializer->unserialize($data));
     }
 
     /**
@@ -45,7 +31,8 @@ public function unserialize()
      */
     public function serialize()
     {
+        $serializer = new NullSerializer();
         $data = ['foo' => 'abc', 'bar' => 123];
-        $this->assertSame($data, $this->serializer->serialize($data));
+        $this->assertSame($data, $serializer->serialize($data));
     }
 }
diff --git a/tests/TTLValidatorTraitTest.php b/tests/TTLValidatorTraitTest.php
index 2eba520..443a5f9 100644
--- a/tests/TTLValidatorTraitTest.php
+++ b/tests/TTLValidatorTraitTest.php
@@ -30,12 +30,12 @@ public function validateTTLWithValidValues($ttl)
      *
      * @return array
      */
-    public function provideValidTTLs()
+    public static function provideValidTTLs()
     {
         return [
-            ['null' => null],
-            ['DateInterval' => \DateInterval::createFromDateString('1 day')],
-            ['int' => 3600],
+            [null],
+            [\DateInterval::createFromDateString('1 day')],
+            [3600],
         ];
     }
 
@@ -60,12 +60,12 @@ public function validateTTLWithInvalidValue($ttl)
      *
      * @return array
      */
-    public function provideInvalidTTLs()
+    public static function provideInvalidTTLs()
     {
         return [
-            ['string' => ''],
-            ['float' => 1.1],
-            ['DdateTime' => new \DateTime()],
+            [''],
+            [1.1],
+            [new \DateTime()],
         ];
     }
 }