diff --git a/.gitignore b/.gitignore
index 7caaf50..b608d69 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
 /vendor
 composer.lock
 clover.xml
+.phpunit.result.cache
+phpunit.xml.bak
diff --git a/.travis.yml b/.travis.yml
index 90481ad..1259d83 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,19 +1,11 @@
 language: php
 
 php:
-  - 5.5
-  - 5.6
-  - 7.0
-  - hhvm
-  - nightly
-
-matrix:
-  allow_failures:
-    - php: 5.5
-    - php: nightly
+  - 7.4
+  - 8.0
 
 install:
   - composer install --dev
 
 script:
-  - vendor/bin/phpunit
\ No newline at end of file
+  - vendor/bin/phpunit
diff --git a/composer.json b/composer.json
index b5647f7..7f91501 100644
--- a/composer.json
+++ b/composer.json
@@ -11,12 +11,12 @@
     ],
     "minimum-stability": "stable",
     "require": {
-        "php": ">=5.6,<8.0-DEV"
+        "php": ">=7.4",
+        "composer-plugin-api": "^1.0.0 || ^2.0.0"
     },
     "require-dev": {
-        "composer/composer": "~1.1",
-        "phpunit/phpunit": "~5.3",
-        "etsy/phpunit-extensions": "0.7.*"
+        "composer/composer": "^2",
+        "phpunit/phpunit": "^9"
     },
     "scripts": {
         "post-package-install": [
diff --git a/phpunit.xml b/phpunit.xml
index fc42835..7c46165 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     bootstrap="./vendor/autoload.php"
     colors="true"
     convertErrorsToExceptions="true"
@@ -9,26 +9,27 @@
     stopOnFailure="false"
     processIsolation="false"
     backupGlobals="false"
-    syntaxCheck="true"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
 >
+    <coverage includeUncoveredFiles="true">
+        <include>
+            <directory suffix=".php">./src</directory>
+        </include>
+        <exclude>
+            <directory>./vendor</directory>
+            <directory>./tests</directory>
+            <directory>./template</directory>
+            <directory>./bin</directory>
+        </exclude>
+        <report>
+            <clover outputFile="./clover.xml"/>
+            <text outputFile="php://stdout" showUncoveredFiles="false"/>
+        </report>
+    </coverage>
     <testsuites>
         <testsuite name="Tests">
             <directory>./tests</directory>
         </testsuite>
     </testsuites>
-    <filter>
-        <whitelist addUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">./src</directory>
-            <exclude>
-                <directory>./vendor</directory>
-                <directory>./tests</directory>
-                <directory>./template</directory>
-                <directory>./bin</directory>
-            </exclude>
-        </whitelist>
-    </filter>
-    <logging>
-        <log type="coverage-text" target="php://stdout" showUncoveredFiles="false"/>
-        <log type="coverage-clover" target="./clover.xml"/>
-    </logging>
-</phpunit>
\ No newline at end of file
+    <logging/>
+</phpunit>
diff --git a/tests/CustomAssertionsTrait.php b/tests/CustomAssertionsTrait.php
new file mode 100644
index 0000000..14fa095
--- /dev/null
+++ b/tests/CustomAssertionsTrait.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace Jenko\Sunscreen\Tests;
+
+trait CustomAssertionsTrait
+{
+    public static function assertStringMatchIgnoreWhitespace( string $expecting, string $actual )
+    {
+        $expected = preg_replace('#\&. #', '', implode(' ', preg_split('/\s+/', trim($expecting))));
+        $actual = preg_replace('#\&. #', '', implode(' ', preg_split('/\s+/', trim($actual))));
+
+        return self::assertEquals(
+            $expected,
+            $actual
+        );
+    }
+}
diff --git a/tests/Guesser/AbstractClassGuesserTest.php b/tests/Guesser/AbstractClassGuesserTest.php
index 44ad739..8365a29 100644
--- a/tests/Guesser/AbstractClassGuesserTest.php
+++ b/tests/Guesser/AbstractClassGuesserTest.php
@@ -5,8 +5,9 @@
 use Composer\Package\Package;
 use Jenko\Sunscreen\Guesser\AbstractClassGuesser;
 use Jenko\Sunscreen\Util;
+use PHPUnit\Framework\TestCase;
 
-class AbstractClassGuesserTest extends \PHPUnit_Framework_TestCase
+class AbstractClassGuesserTest extends TestCase
 {
     /**
      * @dataProvider getAutoloadsAndExpectedClasses
@@ -33,4 +34,4 @@ public function getAutoloadsAndExpectedClasses()
             [['psr-9999' => ['Foo\\Bar\\' => 'foo/bar/src/']], []],
         ];
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Guesser/InterfaceClassGuesserTest.php b/tests/Guesser/InterfaceClassGuesserTest.php
index 552145b..f6920ea 100644
--- a/tests/Guesser/InterfaceClassGuesserTest.php
+++ b/tests/Guesser/InterfaceClassGuesserTest.php
@@ -5,8 +5,9 @@
 use Composer\Package\Package;
 use Jenko\Sunscreen\Guesser\InterfaceGuesser;
 use Jenko\Sunscreen\Util;
+use PHPUnit\Framework\TestCase;
 
-class InterfaceGuesserTest extends \PHPUnit_Framework_TestCase
+class InterfaceGuesserTest extends TestCase
 {
     /**
      * @dataProvider getAutoloadsAndExpectedClasses
@@ -33,4 +34,4 @@ public function getAutoloadsAndExpectedClasses()
             [['psr-9999' => ['Foo\\Bar\\' => 'foo/bar/src/']], []],
         ];
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Processor/AdapterMethodsProcessorTest.php b/tests/Processor/AdapterMethodsProcessorTest.php
index 4884e70..a820550 100644
--- a/tests/Processor/AdapterMethodsProcessorTest.php
+++ b/tests/Processor/AdapterMethodsProcessorTest.php
@@ -3,10 +3,14 @@
 namespace Jenko\Sunscreen\Tests\Processor;
 
 use Jenko\Sunscreen\Processor\AdapterMethodsProcessor;
+use Jenko\Sunscreen\Tests\CustomAssertionsTrait;
 use Jenko\Sunscreen\Tests\Fixtures\Foo;
+use PHPUnit\Framework\TestCase;
 
-class AdapterMethodsProcessorTest extends \PHPUnit_Framework_TestCase
+class AdapterMethodsProcessorTest extends TestCase
 {
+    use CustomAssertionsTrait;
+
     /**
      * @dataProvider getMethodsAndExpectedStrings
      * @param array $methods
@@ -16,7 +20,7 @@ public function testProcessGeneratesExpectedMethodsString($methods, $expectedMet
     {
         $processor = new AdapterMethodsProcessor($methods, 'myInterface');
 
-        \PHPUnit_Extensions_Assert_More::assertStringMatchIgnoreWhitespace(
+        self::assertStringMatchIgnoreWhitespace(
             $expectedMethodsString,
             $processor->process(true)
         );
diff --git a/tests/Processor/AdapterProcessorTest.php b/tests/Processor/AdapterProcessorTest.php
index 3fd6a2e..3463484 100644
--- a/tests/Processor/AdapterProcessorTest.php
+++ b/tests/Processor/AdapterProcessorTest.php
@@ -3,10 +3,14 @@
 namespace Jenko\Sunscreen\Tests\Processor;
 
 use Jenko\Sunscreen\Processor\AdapterProcessor;
+use Jenko\Sunscreen\Tests\CustomAssertionsTrait;
 use Jenko\Sunscreen\Util;
+use PHPUnit\Framework\TestCase;
 
-class AdapterProcessorTest extends \PHPUnit_Framework_TestCase
+class AdapterProcessorTest extends TestCase
 {
+    use CustomAssertionsTrait;
+
     /**
      * @dataProvider getInterfaceAndExpectedStrings
      *
@@ -20,7 +24,7 @@ public function testProcessGeneratesExpectedAdapterString($interfaceFqn, $expect
 
         $processor = new AdapterProcessor($interfaceFqn, $namespace, $fileLocation);
 
-        \PHPUnit_Extensions_Assert_More::assertStringMatchIgnoreWhitespace($expectedAdapterString, $processor->process(true));
+        self::assertStringMatchIgnoreWhitespace($expectedAdapterString, $processor->process(true));
     }
 
     public function getInterfaceAndExpectedStrings()
diff --git a/tests/Processor/ClassProcessorTest.php b/tests/Processor/ClassProcessorTest.php
index ba58ffa..1e35d5b 100644
--- a/tests/Processor/ClassProcessorTest.php
+++ b/tests/Processor/ClassProcessorTest.php
@@ -3,10 +3,14 @@
 namespace Jenko\Sunscreen\Tests\Processor;
 
 use Jenko\Sunscreen\Processor\ClassProcessor;
+use Jenko\Sunscreen\Tests\CustomAssertionsTrait;
 use Jenko\Sunscreen\Util;
+use PHPUnit\Framework\TestCase;
 
-class ClassProcessorTest extends \PHPUnit_Framework_TestCase
+class ClassProcessorTest extends TestCase
 {
+    use CustomAssertionsTrait;
+
     /**
      * @dataProvider getClassAndExpectedStrings
      *
@@ -20,7 +24,7 @@ public function testProcessGeneratesExpectedClassString($classFqn, $expectedClas
 
         $processor = new ClassProcessor($classFqn, $namespace, $fileLocation);
 
-        \PHPUnit_Extensions_Assert_More::assertStringMatchIgnoreWhitespace(
+        self::assertStringMatchIgnoreWhitespace(
             $expectedClassString,
             $processor->process(true)
         );
diff --git a/tests/Processor/InterfaceMethodsProcessorTest.php b/tests/Processor/InterfaceMethodsProcessorTest.php
index f1fd3a4..18e9ea7 100644
--- a/tests/Processor/InterfaceMethodsProcessorTest.php
+++ b/tests/Processor/InterfaceMethodsProcessorTest.php
@@ -3,9 +3,13 @@
 namespace Jenko\Sunscreen\Tests\Processor;
 
 use Jenko\Sunscreen\Processor\InterfaceMethodsProcessor;
+use Jenko\Sunscreen\Tests\CustomAssertionsTrait;
+use PHPUnit\Framework\TestCase;
 
-class InterfaceMethodsProcessorTest extends \PHPUnit_Framework_TestCase
+class InterfaceMethodsProcessorTest extends TestCase
 {
+    use CustomAssertionsTrait;
+
     /**
      * @dataProvider getMethodsAndExpectedStrings
      * @param array $methods
@@ -15,7 +19,7 @@ public function testProcessGeneratesExpectedMethodsString($methods, $expectedMet
     {
         $processor = new InterfaceMethodsProcessor($methods);
 
-        \PHPUnit_Extensions_Assert_More::assertStringMatchIgnoreWhitespace(
+        self::assertStringMatchIgnoreWhitespace(
             $expectedMethodsString,
             $processor->process(true)
         );
diff --git a/tests/Processor/InterfaceProcessorTest.php b/tests/Processor/InterfaceProcessorTest.php
index 3ab6017..8f75081 100644
--- a/tests/Processor/InterfaceProcessorTest.php
+++ b/tests/Processor/InterfaceProcessorTest.php
@@ -3,10 +3,14 @@
 namespace Jenko\Sunscreen\Tests\Processor;
 
 use Jenko\Sunscreen\Processor\InterfaceProcessor;
+use Jenko\Sunscreen\Tests\CustomAssertionsTrait;
 use Jenko\Sunscreen\Util;
+use PHPUnit\Framework\TestCase;
 
-class InterfaceProcessorTest extends \PHPUnit_Framework_TestCase
+class InterfaceProcessorTest extends TestCase
 {
+    use CustomAssertionsTrait;
+
     /**
      * @dataProvider getInterfaceAndExpectedStrings
      *
@@ -20,7 +24,7 @@ public function testProcessGeneratesExpectedInterfaceString($interfaceFqn, $expe
 
         $processor = new InterfaceProcessor($interfaceFqn, $namespace, $fileLocation);
 
-        \PHPUnit_Extensions_Assert_More::assertStringMatchIgnoreWhitespace(
+        self::assertStringMatchIgnoreWhitespace(
             $expectedClassString,
             $processor->process(true)
         );
diff --git a/tests/UtilTest.php b/tests/UtilTest.php
index 60e7c8d..d888db2 100644
--- a/tests/UtilTest.php
+++ b/tests/UtilTest.php
@@ -4,8 +4,9 @@
 
 use Composer\Package\Package;
 use Jenko\Sunscreen\Util;
+use PHPUnit\Framework\TestCase;
 
-class UtilTest extends \PHPUnit_Framework_TestCase
+class UtilTest extends TestCase
 {
     /**
      * @dataProvider getAutoloadsAndExpectedNamespaces
@@ -77,4 +78,4 @@ public function getInterfaceFqnAndExpectedClassName()
             ['Jenko\Sunscreen\Tests\Fixtures\BazInterface', 'JenkoBaz']
         ];
     }
-}
\ No newline at end of file
+}