diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 9cddbba..c94aa09 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: ['7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4', '8.5']
+        php: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4', '8.5']
 
     steps:
       - uses: actions/checkout@v2
diff --git a/composer.json b/composer.json
index 6f7b045..e9d6ea8 100644
--- a/composer.json
+++ b/composer.json
@@ -21,12 +21,12 @@
     },
     "require": {
         "php": ">=7.1",
-        "composer-plugin-api": "^1.0 || ^2.0"
+        "composer-plugin-api": "^2.0"
     },
     "require-dev": {
-        "composer/composer": "^1.1@dev || ^2.0@dev",
+        "composer/composer": "^2.0@dev",
         "mikey179/vfsstream": "~1.4.0@dev",
-        "phpunit/phpunit": ">4.8 <9"
+        "phpunit/phpunit": "^8 || ^9"
     },
     "replace": {
         "helhum/class-alias-loader": "*"
diff --git a/tests/Unit/BaseTestCase.php b/tests/Unit/BaseTestCase.php
deleted file mode 100644
index 36dc405..0000000
--- a/tests/Unit/BaseTestCase.php
+++ /dev/null
@@ -1,17 +0,0 @@
-<?php
-
-namespace TYPO3\ClassAliasLoader\Test\Unit;
-
-use PHPUnit\Framework\TestCase;
-
-if (class_exists('PHPUnit_Framework_TestCase')) {
-class BaseTestCase extends \PHPUnit_Framework_TestCase
-{
-
-}
-} else {
-class BaseTestCase extends TestCase
-{
-
-}
-}
diff --git a/tests/Unit/ClassAliasLoaderTest.php b/tests/Unit/ClassAliasLoaderTest.php
index bc8d5c6..f1247e7 100644
--- a/tests/Unit/ClassAliasLoaderTest.php
+++ b/tests/Unit/ClassAliasLoaderTest.php
@@ -12,12 +12,13 @@
 
 use Composer\Autoload\ClassLoader as ComposerClassLoader;
 use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
 use TYPO3\ClassAliasLoader\ClassAliasLoader;
 
 /**
  * Test case for ClassAliasLoader
  */
-class ClassAliasLoaderTest extends BaseTestCase
+class ClassAliasLoaderTest extends TestCase
 {
     /**
      * @var ClassAliasLoader
@@ -25,23 +26,17 @@ class ClassAliasLoaderTest extends BaseTestCase
     protected $subject;
 
     /**
-     * @var ComposerClassLoader|MockObject|PHPUnit_Framework_MockObject_MockObject
+     * @var ComposerClassLoader|MockObject
      */
     protected $composerClassLoaderMock;
 
-    /**
-     * @before
-     */
-    public function setMeUp()
+    public function setUp(): void
     {
         $this->composerClassLoaderMock = $this->getMockBuilder('Composer\\Autoload\\ClassLoader')->getMock();
         $this->subject = new ClassAliasLoader($this->composerClassLoaderMock);
     }
 
-    /**
-     * @after
-     */
-    public function tearMeDown()
+    public function tearDown(): void
     {
         $this->subject->unregister();
     }
@@ -49,7 +44,7 @@ public function tearMeDown()
     /**
      * @test
      */
-    public function composerLoadClassIsCalledOnlyOnceWhenCaseSensitiveClassLoadingIsOn()
+    public function composerLoadClassIsCalledOnlyOnceWhenCaseSensitiveClassLoadingIsOn(): void
     {
         $this->composerClassLoaderMock->expects($this->once())->method('loadClass');
         $this->subject->loadClassWithAlias('TestClass');
@@ -58,7 +53,7 @@ public function composerLoadClassIsCalledOnlyOnceWhenCaseSensitiveClassLoadingIs
     /**
      * @test
      */
-    public function composerLoadClassIsCalledOnlyOnceWhenCaseSensitiveClassLoadingIsOffButClassIsFound()
+    public function composerLoadClassIsCalledOnlyOnceWhenCaseSensitiveClassLoadingIsOffButClassIsFound(): void
     {
         $this->composerClassLoaderMock->expects($this->once())->method('loadClass')->willReturn(true);
         $this->subject->setCaseSensitiveClassLoading(false);
@@ -68,7 +63,7 @@ public function composerLoadClassIsCalledOnlyOnceWhenCaseSensitiveClassLoadingIs
     /**
      * @test
      */
-    public function composerLoadClassIsCalledTwiceWhenCaseSensitiveClassLoadingIsOffAndClassIsNotFound()
+    public function composerLoadClassIsCalledTwiceWhenCaseSensitiveClassLoadingIsOffAndClassIsNotFound(): void
     {
         $this->composerClassLoaderMock->expects($this->exactly(2))->method('loadClass');
         $this->subject->setCaseSensitiveClassLoading(false);
@@ -78,7 +73,7 @@ public function composerLoadClassIsCalledTwiceWhenCaseSensitiveClassLoadingIsOff
     /**
      * @test
      */
-    public function loadsClassIfNoAliasIsFound()
+    public function loadsClassIfNoAliasIsFound(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $this->composerClassLoaderMock->expects($this->once())->method('loadClass')->willReturnCallback(function ($className) {
@@ -92,7 +87,7 @@ public function loadsClassIfNoAliasIsFound()
     /**
      * @test
      */
-    public function callingLoadClassMultipleTimesInEdgeCasesWillStillWork()
+    public function callingLoadClassMultipleTimesInEdgeCasesWillStillWork(): void
     {
         $this->composerClassLoaderMock
             ->expects($this->exactly(2))
@@ -105,7 +100,7 @@ public function callingLoadClassMultipleTimesInEdgeCasesWillStillWork()
     /**
      * @test
      */
-    public function loadClassWithOriginalClassNameSetsAliases()
+    public function loadClassWithOriginalClassNameSetsAliases(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -134,7 +129,7 @@ public function loadClassWithOriginalClassNameSetsAliases()
     /**
      * @test
      */
-    public function getClassNameForAliasReturnsClassNameForEachAlias()
+    public function getClassNameForAliasReturnsClassNameForEachAlias(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -157,7 +152,7 @@ public function getClassNameForAliasReturnsClassNameForEachAlias()
     /**
      * @test
      */
-    public function addAliasMapAddsAliasesCorrectlyToTheMap()
+    public function addAliasMapAddsAliasesCorrectlyToTheMap(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -185,7 +180,7 @@ public function addAliasMapAddsAliasesCorrectlyToTheMap()
     /**
      * @test
      */
-    public function getClassNameForAliasReturnsClassNameForClassName()
+    public function getClassNameForAliasReturnsClassNameForClassName(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -207,7 +202,7 @@ public function getClassNameForAliasReturnsClassNameForClassName()
     /**
      * @test
      */
-    public function getClassNameForAliasReturnsClassNameForClassNameWithNoAliasMapSet()
+    public function getClassNameForAliasReturnsClassNameForClassNameWithNoAliasMapSet(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $this->assertEquals($testClassName, $this->subject->getClassNameForAlias($testClassName));
@@ -216,7 +211,7 @@ public function getClassNameForAliasReturnsClassNameForClassNameWithNoAliasMapSe
     /**
      * @test
      */
-    public function loadClassWithAliasClassNameSetsAliasesAndLoadsOriginalClass()
+    public function loadClassWithAliasClassNameSetsAliasesAndLoadsOriginalClass(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -246,7 +241,7 @@ public function loadClassWithAliasClassNameSetsAliasesAndLoadsOriginalClass()
     /**
      * @test
      */
-    public function aliasesInstancesHaveOriginalClassName()
+    public function aliasesInstancesHaveOriginalClassName(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -279,7 +274,7 @@ public function aliasesInstancesHaveOriginalClassName()
     /**
      * @test
      */
-    public function classAliasesAreGracefullySetIfClassAlreadyExists()
+    public function classAliasesAreGracefullySetIfClassAlreadyExists(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -310,7 +305,7 @@ public function classAliasesAreGracefullySetIfClassAlreadyExists()
     /**
      * @test
      */
-    public function interfaceAliasesAreGracefullySetIfInterfaceAlreadyExists()
+    public function interfaceAliasesAreGracefullySetIfInterfaceAlreadyExists(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -338,7 +333,7 @@ public function interfaceAliasesAreGracefullySetIfInterfaceAlreadyExists()
     /**
      * @test
      */
-    public function classAliasesAreNotReEstablishedIfTheyAlreadyExist()
+    public function classAliasesAreNotReEstablishedIfTheyAlreadyExist(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
@@ -366,7 +361,7 @@ class_alias($testClassName, $testAlias1);
     /**
      * @test
      */
-    public function loadClassWithAliasReturnsNullIfComposerClassLoaderCannotFindClass()
+    public function loadClassWithAliasReturnsNullIfComposerClassLoaderCannotFindClass(): void
     {
         $this->composerClassLoaderMock->expects($this->once())->method('loadClass');
         $this->assertNull($this->subject->loadClassWithAlias('TestClass'));
@@ -375,7 +370,7 @@ public function loadClassWithAliasReturnsNullIfComposerClassLoaderCannotFindClas
     /**
      * @test
      */
-    public function loadClassWithAliasReturnsNullIfComposerClassLoaderCannotFindClassEvenIfItExistsInMap()
+    public function loadClassWithAliasReturnsNullIfComposerClassLoaderCannotFindClassEvenIfItExistsInMap(): void
     {
         $testClassName = 'TestClass' . md5(uniqid('bla', true));
         $testAlias1 = 'TestAlias' . md5(uniqid('bla', true));
diff --git a/tests/Unit/ConfigTest.php b/tests/Unit/ConfigTest.php
index 9be449b..d4dc111 100644
--- a/tests/Unit/ConfigTest.php
+++ b/tests/Unit/ConfigTest.php
@@ -12,12 +12,14 @@
 
 use Composer\IO\IOInterface;
 use Composer\Package\PackageInterface;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
 use TYPO3\ClassAliasLoader\Config;
 
 /**
  * Test case for Config
  */
-class ConfigTest extends BaseTestCase
+class ConfigTest extends TestCase
 {
     /**
      * @var Config
@@ -25,30 +27,26 @@ class ConfigTest extends BaseTestCase
     protected $subject;
 
     /**
-     * @var IOInterface|\PHPUnit_Framework_MockObject_MockObject
+     * @var IOInterface|MockObject
      */
     protected $ioMock;
 
     /**
-     * @var PackageInterface|\PHPUnit_Framework_MockObject_MockObject
+     * @var PackageInterface|MockObject
      */
     protected $packageMock;
 
-    /**
-     * @before
-     */
-    public function setMeUp()
+    public function setUp(): void
     {
         $this->ioMock = $this->getMockBuilder('Composer\\IO\\IOInterface')->getMock();
         $this->packageMock = $this->getMockBuilder('Composer\\Package\\PackageInterface')->getMock();
-
         $this->subject = new Config($this->packageMock, $this->ioMock);
     }
 
     /**
      * @test
      */
-    public function throwsExceptionForEmptyKey()
+    public function throwsExceptionForEmptyKey(): void
     {
         // Use this instead when old PHP versions are dropped and minimum phpunit version can be raised:
         /**
@@ -70,7 +68,7 @@ public function throwsExceptionForEmptyKey()
     /**
      * @test
      */
-    public function defaultConfigIsAppliedWhenNothingIsConfiguredInPackage()
+    public function defaultConfigIsAppliedWhenNothingIsConfiguredInPackage(): void
     {
         $this->assertFalse($this->subject->get('always-add-alias-loader'));
         $this->assertTrue($this->subject->get('autoload-case-sensitivity'));
@@ -80,7 +78,7 @@ public function defaultConfigIsAppliedWhenNothingIsConfiguredInPackage()
     /**
      * @test
      */
-    public function aliasMapConfigIsExtracted()
+    public function aliasMapConfigIsExtracted(): void
     {
         $this->packageMock->expects($this->any())->method('getExtra')->willReturn(
             array(
@@ -100,7 +98,7 @@ public function aliasMapConfigIsExtracted()
     /**
      * @test
      */
-    public function aliasMapConfigIsExtractedFromDeprecatedKey()
+    public function aliasMapConfigIsExtractedFromDeprecatedKey(): void
     {
         $this->packageMock->expects($this->any())->method('getExtra')->willReturn(
             array(
@@ -121,7 +119,7 @@ public function aliasMapConfigIsExtractedFromDeprecatedKey()
     /**
      * @test
      */
-    public function otherConfigIsExtracted()
+    public function otherConfigIsExtracted(): void
     {
         $this->packageMock->expects($this->any())->method('getExtra')->willReturn(
             array(
@@ -141,7 +139,7 @@ public function otherConfigIsExtracted()
     /**
      * @test
      */
-    public function otherConfigIsExtractedFromDeprecatedKey()
+    public function otherConfigIsExtractedFromDeprecatedKey(): void
     {
         $this->packageMock->expects($this->any())->method('getExtra')->willReturn(
             array(
@@ -161,7 +159,7 @@ public function otherConfigIsExtractedFromDeprecatedKey()
     /**
      * @test
      */
-    public function caseSensitivityConfigIsExtractedFromVeryDeprecatedKey()
+    public function caseSensitivityConfigIsExtractedFromVeryDeprecatedKey(): void
     {
         $this->packageMock->expects($this->any())->method('getExtra')->willReturn(
             array(
diff --git a/tests/Unit/IncludeFileTest.php b/tests/Unit/IncludeFileTest.php
index 03fb319..c3ae857 100644
--- a/tests/Unit/IncludeFileTest.php
+++ b/tests/Unit/IncludeFileTest.php
@@ -14,13 +14,14 @@
 use Composer\IO\IOInterface;
 use Composer\Package\PackageInterface;
 use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
 use TYPO3\ClassAliasLoader\Config;
 use TYPO3\ClassAliasLoader\IncludeFile;
 
 /**
  * Test case for IncludeFile
  */
-final class IncludeFileTest extends BaseTestCase
+final class IncludeFileTest extends TestCase
 {
     /**
      * @var IncludeFile
@@ -44,10 +45,7 @@ final class IncludeFileTest extends BaseTestCase
 
     private $testDir = __DIR__;
 
-    /**
-     * @before
-     */
-    public function setMeUp()
+    public function setUp(): void
     {
         $this->ioMock = $this->getMockBuilder('Composer\\IO\\IOInterface')->getMock();
         $this->packageMock = $this->getMockBuilder('Composer\\Package\\RootPackageInterface')->getMock();
@@ -84,17 +82,14 @@ public function setMeUp()
         );
     }
 
-    /**
-     * @after
-     */
-    public function tearMeDown()
+    public function tearDown(): void
     {
         unlink($this->testDir . IncludeFile::INCLUDE_FILE);
         rmdir(dirname($this->testDir . IncludeFile::INCLUDE_FILE));
     }
 
 
-    public function testIncludeFileCanPeWritten()
+    public function testIncludeFileCanPeWritten(): void
     {
         $this->subject->register();
         self::assertTrue(file_exists($this->testDir . IncludeFile::INCLUDE_FILE));