diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6bb75f0..a13804b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,6 +11,7 @@ jobs:
     strategy:
       matrix:
         php:
+          - 8.0
           - 7.4
           - 7.3
           - 7.2
@@ -27,6 +28,9 @@ jobs:
           coverage: xdebug
       - run: composer install
       - run: vendor/bin/phpunit --coverage-text
+        if: ${{ matrix.php >= 7.3 }}
+      - run: vendor/bin/phpunit --coverage-text -c phpunit.xml.legacy
+        if: ${{ matrix.php < 7.3 }}
 
   PHPUnit-hhvm:
     name: PHPUnit (HHVM)
diff --git a/composer.json b/composer.json
index 76aa6c3..e488fa6 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
       , "ratchet/rfc6455": "^0.3"
     }
   , "require-dev": {
-        "phpunit/phpunit": "~4.8"
+        "phpunit/phpunit": "^9.3 || ^5.7 || ^4.8"
     }
   , "suggest": {
         "reactivex/rxphp": "~2.0"
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index e23d1d5..08c041f 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,24 +1,22 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit
-        forceCoversAnnotation="true"
-        mapTestClassNameToCoveredClassName="true"
-        bootstrap="tests/bootstrap.php"
-        colors="true"
+
+<!-- PHPUnit configuration file with new format for PHPUnit 9.3+ -->
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
+        xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
         backupGlobals="false"
         backupStaticAttributes="false"
-        syntaxCheck="false"
-        stopOnError="false"
->
-
+        bootstrap="vendor/autoload.php"
+        cacheResult="false"
+        colors="true"
+        stopOnError="false">
     <testsuites>
         <testsuite name="unit">
-            <directory>./tests/unit/</directory>
+            <directory>./tests/</directory>
         </testsuite>
     </testsuites>
-
-    <filter>
-        <whitelist>
+    <coverage>
+        <include>
             <directory>./src/</directory>
-        </whitelist>
-    </filter>
-</phpunit>
\ No newline at end of file
+        </include>
+    </coverage>
+</phpunit>
diff --git a/phpunit.xml.legacy b/phpunit.xml.legacy
new file mode 100644
index 0000000..dd7205b
--- /dev/null
+++ b/phpunit.xml.legacy
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!-- PHPUnit configuration file with old format for PHPUnit 9.2 or older -->
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+        xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/4.8/phpunit.xsd"
+        backupGlobals="false"
+        backupStaticAttributes="false"
+        bootstrap="vendor/autoload.php"
+        cacheResult="false"
+        colors="true"
+        stopOnError="false">
+    <testsuites>
+        <testsuite name="unit">
+            <directory>./tests/</directory>
+        </testsuite>
+    </testsuites>
+    <filter>
+        <whitelist>
+            <directory>./src/</directory>
+        </whitelist>
+    </filter>
+</phpunit>
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
deleted file mode 100644
index d21c14d..0000000
--- a/tests/bootstrap.php
+++ /dev/null
@@ -1,3 +0,0 @@
-<?php
-
-require __DIR__ . '/../vendor/autoload.php';
diff --git a/tests/unit/ConnectorTest.php b/tests/unit/ConnectorTest.php
index 66ef392..a32a051 100644
--- a/tests/unit/ConnectorTest.php
+++ b/tests/unit/ConnectorTest.php
@@ -23,7 +23,7 @@ public function uriDataProvider() {
     public function testSecureConnectionUsesTlsScheme($uri, $expectedConnectorUri) {
         $loop = Factory::create();
 
-        $connector = $this->getMock('React\Socket\ConnectorInterface');
+        $connector = $this->getMockBuilder('React\Socket\ConnectorInterface')->getMock();
 
         $connector->expects($this->once())
             ->method('connect')