diff --git a/src/Symfony/Bridge/PhpUnit/CHANGELOG.md b/src/Symfony/Bridge/PhpUnit/CHANGELOG.md
index 92907ea25c..b85364ad7d 100644
--- a/src/Symfony/Bridge/PhpUnit/CHANGELOG.md
+++ b/src/Symfony/Bridge/PhpUnit/CHANGELOG.md
@@ -6,6 +6,7 @@ CHANGELOG
 
  * made the bridge act as a polyfill for newest PHPUnit features
  * added `SetUpTearDownTrait` to allow working around the `void` return-type added by PHPUnit 8
+ * added namespace aliases for PHPUnit < 6
 
 4.3.0
 -----
diff --git a/src/Symfony/Bridge/PhpUnit/CoverageListener.php b/src/Symfony/Bridge/PhpUnit/CoverageListener.php
index d41c26968f..805f9222a5 100644
--- a/src/Symfony/Bridge/PhpUnit/CoverageListener.php
+++ b/src/Symfony/Bridge/PhpUnit/CoverageListener.php
@@ -11,7 +11,7 @@
 
 namespace Symfony\Bridge\PhpUnit;
 
-if (class_exists('PHPUnit_Runner_Version') && version_compare(\PHPUnit_Runner_Version::id(), '6.0.0', '<')) {
+if (version_compare(\PHPUnit\Runner\Version::id(), '6.0.0', '<')) {
     class_alias('Symfony\Bridge\PhpUnit\Legacy\CoverageListenerForV5', 'Symfony\Bridge\PhpUnit\CoverageListener');
 } elseif (version_compare(\PHPUnit\Runner\Version::id(), '7.0.0', '<')) {
     class_alias('Symfony\Bridge\PhpUnit\Legacy\CoverageListenerForV6', 'Symfony\Bridge\PhpUnit\CoverageListener');
diff --git a/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler.php b/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler.php
index e059fe2a9d..ca2805b923 100644
--- a/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler.php
+++ b/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Bridge\PhpUnit;
 
+use PHPUnit\Util\ErrorHandler;
 use Symfony\Bridge\PhpUnit\DeprecationErrorHandler\Configuration;
 use Symfony\Bridge\PhpUnit\DeprecationErrorHandler\Deprecation;
 
@@ -48,7 +49,6 @@ class DeprecationErrorHandler
     ];
 
     private static $isRegistered = false;
-    private static $utilPrefix;
 
     /**
      * Registers and configures the deprecation handler.
@@ -72,15 +72,13 @@ class DeprecationErrorHandler
             return;
         }
 
-        self::$utilPrefix = class_exists('PHPUnit_Util_ErrorHandler') ? 'PHPUnit_Util_' : 'PHPUnit\Util\\';
-
         $handler = new self();
         $oldErrorHandler = set_error_handler([$handler, 'handleError']);
 
         if (null !== $oldErrorHandler) {
             restore_error_handler();
 
-            if ([self::$utilPrefix.'ErrorHandler', 'handleError'] === $oldErrorHandler) {
+            if ([ErrorHandler::class, 'handleError'] === $oldErrorHandler) {
                 restore_error_handler();
                 self::register($mode);
             }
@@ -100,12 +98,7 @@ class DeprecationErrorHandler
                     return $previousErrorHandler($type, $msg, $file, $line, $context);
                 }
 
-                static $autoload = true;
-
-                $ErrorHandler = class_exists('PHPUnit_Util_ErrorHandler', $autoload) ? 'PHPUnit_Util_ErrorHandler' : 'PHPUnit\Util\ErrorHandler';
-                $autoload = false;
-
-                return $ErrorHandler::handleError($type, $msg, $file, $line, $context);
+                return ErrorHandler::handleError($type, $msg, $file, $line, $context);
             }
 
             $deprecations[] = [error_reporting(), $msg, $file];
@@ -122,9 +115,7 @@ class DeprecationErrorHandler
     public function handleError($type, $msg, $file, $line, $context = [])
     {
         if ((E_USER_DEPRECATED !== $type && E_DEPRECATED !== $type) || !$this->getConfiguration()->isEnabled()) {
-            $ErrorHandler = self::$utilPrefix.'ErrorHandler';
-
-            return $ErrorHandler::handleError($type, $msg, $file, $line, $context);
+            return ErrorHandler::handleError($type, $msg, $file, $line, $context);
         }
 
         $deprecation = new Deprecation($msg, debug_backtrace(), $file);
@@ -140,7 +131,7 @@ class DeprecationErrorHandler
 
             if (0 !== error_reporting()) {
                 $group = 'unsilenced';
-            } elseif ($deprecation->isLegacy(self::$utilPrefix)) {
+            } elseif ($deprecation->isLegacy()) {
                 $group = 'legacy';
             } else {
                 $group = [
diff --git a/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler/Deprecation.php b/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler/Deprecation.php
index 2d6aa29224..e5d2dc35d7 100644
--- a/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler/Deprecation.php
+++ b/src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler/Deprecation.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Bridge\PhpUnit\DeprecationErrorHandler;
 
+use PHPUnit\Util\Test;
 use Symfony\Bridge\PhpUnit\Legacy\SymfonyTestsListenerFor;
 
 /**
@@ -156,9 +157,8 @@ class Deprecation
      *
      * @return bool
      */
-    public function isLegacy($utilPrefix)
+    public function isLegacy()
     {
-        $test = $utilPrefix.'Test';
         $class = $this->originatingClass();
         $method = $this->originatingMethod();
 
@@ -166,7 +166,7 @@ class Deprecation
             || 0 === strpos($method, 'provideLegacy')
             || 0 === strpos($method, 'getLegacy')
             || strpos($class, '\Legacy')
-            || \in_array('legacy', $test::getGroups($class, $method), true);
+            || \in_array('legacy', Test::getGroups($class, $method), true);
     }
 
     /**
diff --git a/src/Symfony/Bridge/PhpUnit/Legacy/CoverageListenerTrait.php b/src/Symfony/Bridge/PhpUnit/Legacy/CoverageListenerTrait.php
index 52d28cfbf8..1817004bf9 100644
--- a/src/Symfony/Bridge/PhpUnit/Legacy/CoverageListenerTrait.php
+++ b/src/Symfony/Bridge/PhpUnit/Legacy/CoverageListenerTrait.php
@@ -13,6 +13,7 @@ namespace Symfony\Bridge\PhpUnit\Legacy;
 
 use PHPUnit\Framework\TestCase;
 use PHPUnit\Framework\Warning;
+use PHPUnit\Util\Test;
 
 /**
  * PHP 5.3 compatible trait-like shared implementation.
@@ -65,12 +66,7 @@ class CoverageListenerTrait
             return;
         }
 
-        $testClass = \PHPUnit\Util\Test::class;
-        if (!class_exists($testClass, false)) {
-            $testClass = \PHPUnit_Util_Test::class;
-        }
-
-        $r = new \ReflectionProperty($testClass, 'annotationCache');
+        $r = new \ReflectionProperty(Test::class, 'annotationCache');
         $r->setAccessible(true);
 
         $cache = $r->getValue();
@@ -79,7 +75,7 @@ class CoverageListenerTrait
                 'covers' => \is_array($sutFqcn) ? $sutFqcn : array($sutFqcn),
             ),
         ));
-        $r->setValue($testClass, $cache);
+        $r->setValue(Test::class, $cache);
     }
 
     private function findSutFqcn($test)
diff --git a/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillTestCaseTrait.php b/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillTestCaseTrait.php
index 69609c5ea4..5331b3af55 100644
--- a/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillTestCaseTrait.php
+++ b/src/Symfony/Bridge/PhpUnit/Legacy/PolyfillTestCaseTrait.php
@@ -66,7 +66,7 @@ trait PolyfillTestCaseTrait
      */
     public function expectException($exception)
     {
-        $property = new \ReflectionProperty(class_exists('PHPUnit_Framework_TestCase') ? 'PHPUnit_Framework_TestCase' : TestCase::class, 'expectedException');
+        $property = new \ReflectionProperty(TestCase::class, 'expectedException');
         $property->setAccessible(true);
         $property->setValue($this, $exception);
     }
@@ -78,7 +78,7 @@ trait PolyfillTestCaseTrait
      */
     public function expectExceptionCode($code)
     {
-        $property = new \ReflectionProperty(class_exists('PHPUnit_Framework_TestCase') ? 'PHPUnit_Framework_TestCase' : TestCase::class, 'expectedExceptionCode');
+        $property = new \ReflectionProperty(TestCase::class, 'expectedExceptionCode');
         $property->setAccessible(true);
         $property->setValue($this, $code);
     }
@@ -90,7 +90,7 @@ trait PolyfillTestCaseTrait
      */
     public function expectExceptionMessage($message)
     {
-        $property = new \ReflectionProperty(class_exists('PHPUnit_Framework_TestCase') ? 'PHPUnit_Framework_TestCase' : TestCase::class, 'expectedExceptionMessage');
+        $property = new \ReflectionProperty(TestCase::class, 'expectedExceptionMessage');
         $property->setAccessible(true);
         $property->setValue($this, $message);
     }
@@ -102,7 +102,7 @@ trait PolyfillTestCaseTrait
      */
     public function expectExceptionMessageRegExp($messageRegExp)
     {
-        $property = new \ReflectionProperty(class_exists('PHPUnit_Framework_TestCase') ? 'PHPUnit_Framework_TestCase' : TestCase::class, 'expectedExceptionMessageRegExp');
+        $property = new \ReflectionProperty(TestCase::class, 'expectedExceptionMessageRegExp');
         $property->setAccessible(true);
         $property->setValue($this, $messageRegExp);
     }
diff --git a/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php b/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
index 803f7114b8..0ac3ee4a1b 100644
--- a/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
+++ b/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
@@ -15,7 +15,9 @@ use Doctrine\Common\Annotations\AnnotationRegistry;
 use PHPUnit\Framework\AssertionFailedError;
 use PHPUnit\Framework\TestCase;
 use PHPUnit\Framework\TestSuite;
+use PHPUnit\Runner\BaseTestRunner;
 use PHPUnit\Util\Blacklist;
+use PHPUnit\Util\Test;
 use Symfony\Bridge\PhpUnit\ClockMock;
 use Symfony\Bridge\PhpUnit\DnsMock;
 use Symfony\Component\Debug\DebugClassLoader as LegacyDebugClassLoader;
@@ -48,11 +50,7 @@ class SymfonyTestsListenerTrait
      */
     public function __construct(array $mockedNamespaces = array())
     {
-        if (class_exists('PHPUnit_Util_Blacklist')) {
-            \PHPUnit_Util_Blacklist::$blacklistedClassNames['\Symfony\Bridge\PhpUnit\Legacy\SymfonyTestsListenerTrait'] = 2;
-        } else {
-            Blacklist::$blacklistedClassNames['\Symfony\Bridge\PhpUnit\Legacy\SymfonyTestsListenerTrait'] = 2;
-        }
+        Blacklist::$blacklistedClassNames['\Symfony\Bridge\PhpUnit\Legacy\SymfonyTestsListenerTrait'] = 2;
 
         $enableDebugClassLoader = class_exists(DebugClassLoader::class) || class_exists(LegacyDebugClassLoader::class);
 
@@ -113,11 +111,6 @@ class SymfonyTestsListenerTrait
 
     public function startTestSuite($suite)
     {
-        if (class_exists('PHPUnit_Util_Blacklist', false)) {
-            $Test = 'PHPUnit_Util_Test';
-        } else {
-            $Test = 'PHPUnit\Util\Test';
-        }
         $suiteName = $suite->getName();
         $this->testsWithWarnings = array();
 
@@ -125,7 +118,7 @@ class SymfonyTestsListenerTrait
             if (!($test instanceof \PHPUnit\Framework\TestCase || $test instanceof TestCase)) {
                 continue;
             }
-            if (null === $Test::getPreserveGlobalStateSettings(\get_class($test), $test->getName(false))) {
+            if (null === Test::getPreserveGlobalStateSettings(\get_class($test), $test->getName(false))) {
                 $test->setPreserveGlobalState(false);
             }
         }
@@ -157,12 +150,12 @@ class SymfonyTestsListenerTrait
             $testSuites = array($suite);
             for ($i = 0; isset($testSuites[$i]); ++$i) {
                 foreach ($testSuites[$i]->tests() as $test) {
-                    if ($test instanceof \PHPUnit_Framework_TestSuite || $test instanceof TestSuite) {
+                    if ($test instanceof TestSuite) {
                         if (!class_exists($test->getName(), false)) {
                             $testSuites[] = $test;
                             continue;
                         }
-                        $groups = $Test::getGroups($test->getName());
+                        $groups = Test::getGroups($test->getName());
                         if (\in_array('time-sensitive', $groups, true)) {
                             ClockMock::register($test->getName());
                         }
@@ -213,14 +206,7 @@ class SymfonyTestsListenerTrait
                 putenv('SYMFONY_DEPRECATIONS_SERIALIZE='.$this->runsInSeparateProcess);
             }
 
-            if (class_exists('PHPUnit_Util_Blacklist', false)) {
-                $Test = 'PHPUnit_Util_Test';
-                $AssertionFailedError = 'PHPUnit_Framework_AssertionFailedError';
-            } else {
-                $Test = 'PHPUnit\Util\Test';
-                $AssertionFailedError = 'PHPUnit\Framework\AssertionFailedError';
-            }
-            $groups = $Test::getGroups(\get_class($test), $test->getName(false));
+            $groups = Test::getGroups(\get_class($test), $test->getName(false));
 
             if (!$this->runsInSeparateProcess) {
                 if (\in_array('time-sensitive', $groups, true)) {
@@ -232,14 +218,14 @@ class SymfonyTestsListenerTrait
                 }
             }
 
-            $annotations = $Test::parseTestMethodAnnotations(\get_class($test), $test->getName(false));
+            $annotations = Test::parseTestMethodAnnotations(\get_class($test), $test->getName(false));
 
             if (isset($annotations['class']['expectedDeprecation'])) {
-                $test->getTestResultObject()->addError($test, new $AssertionFailedError('`@expectedDeprecation` annotations are not allowed at the class level.'), 0);
+                $test->getTestResultObject()->addError($test, new AssertionFailedError('`@expectedDeprecation` annotations are not allowed at the class level.'), 0);
             }
             if (isset($annotations['method']['expectedDeprecation'])) {
                 if (!\in_array('legacy', $groups, true)) {
-                    $this->error = new $AssertionFailedError('Only tests with the `@group legacy` annotation can have `@expectedDeprecation`.');
+                    $this->error = new AssertionFailedError('Only tests with the `@group legacy` annotation can have `@expectedDeprecation`.');
                 }
 
                 $test->getTestResultObject()->beStrictAboutTestsThatDoNotTestAnything(false);
@@ -259,18 +245,8 @@ class SymfonyTestsListenerTrait
 
     public function endTest($test, $time)
     {
-        if (class_exists('PHPUnit_Util_Blacklist', false)) {
-            $Test = 'PHPUnit_Util_Test';
-            $BaseTestRunner = 'PHPUnit_Runner_BaseTestRunner';
-            $Warning = 'PHPUnit_Framework_Warning';
-        } else {
-            $Test = 'PHPUnit\Util\Test';
-            $BaseTestRunner = 'PHPUnit\Runner\BaseTestRunner';
-            $Warning = 'PHPUnit\Framework\Warning';
-        }
         $className = \get_class($test);
-        $classGroups = $Test::getGroups($className);
-        $groups = $Test::getGroups($className, $test->getName(false));
+        $groups = Test::getGroups($className, $test->getName(false));
 
         if (null !== $this->reportUselessTests) {
             $test->getTestResultObject()->beStrictAboutTestsThatDoNotTestAnything($this->reportUselessTests);
@@ -299,20 +275,18 @@ class SymfonyTestsListenerTrait
         }
 
         if ($this->expectedDeprecations) {
-            if (!\in_array($test->getStatus(), array($BaseTestRunner::STATUS_SKIPPED, $BaseTestRunner::STATUS_INCOMPLETE), true)) {
+            if (!\in_array($test->getStatus(), array(BaseTestRunner::STATUS_SKIPPED, BaseTestRunner::STATUS_INCOMPLETE), true)) {
                 $test->addToAssertionCount(\count($this->expectedDeprecations));
             }
 
             restore_error_handler();
 
-            if (!$errored && !\in_array($test->getStatus(), array($BaseTestRunner::STATUS_SKIPPED, $BaseTestRunner::STATUS_INCOMPLETE, $BaseTestRunner::STATUS_FAILURE, $BaseTestRunner::STATUS_ERROR), true)) {
+            if (!$errored && !\in_array($test->getStatus(), array(BaseTestRunner::STATUS_SKIPPED, BaseTestRunner::STATUS_INCOMPLETE, BaseTestRunner::STATUS_FAILURE, BaseTestRunner::STATUS_ERROR), true)) {
                 try {
                     $prefix = "@expectedDeprecation:\n";
                     $test->assertStringMatchesFormat($prefix.'%A  '.implode("\n%A  ", $this->expectedDeprecations)."\n%A", $prefix.'  '.implode("\n  ", $this->gatheredDeprecations)."\n");
                 } catch (AssertionFailedError $e) {
                     $test->getTestResultObject()->addFailure($test, $e, $time);
-                } catch (\PHPUnit_Framework_AssertionFailedError $e) {
-                    $test->getTestResultObject()->addFailure($test, $e, $time);
                 }
             }
 
diff --git a/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php b/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php
index a753525b76..d3cd7563bd 100644
--- a/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php
+++ b/src/Symfony/Bridge/PhpUnit/SymfonyTestsListener.php
@@ -11,7 +11,7 @@
 
 namespace Symfony\Bridge\PhpUnit;
 
-if (class_exists('PHPUnit_Runner_Version') && version_compare(\PHPUnit_Runner_Version::id(), '6.0.0', '<')) {
+if (version_compare(\PHPUnit\Runner\Version::id(), '6.0.0', '<')) {
     class_alias('Symfony\Bridge\PhpUnit\Legacy\SymfonyTestsListenerForV5', 'Symfony\Bridge\PhpUnit\SymfonyTestsListener');
 } elseif (version_compare(\PHPUnit\Runner\Version::id(), '7.0.0', '<')) {
     class_alias('Symfony\Bridge\PhpUnit\Legacy\SymfonyTestsListenerForV6', 'Symfony\Bridge\PhpUnit\SymfonyTestsListener');
diff --git a/src/Symfony/Bridge/PhpUnit/Tests/Fixtures/coverage/tests/bootstrap.php b/src/Symfony/Bridge/PhpUnit/Tests/Fixtures/coverage/tests/bootstrap.php
index 241006431a..3e45381dce 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/Fixtures/coverage/tests/bootstrap.php
+++ b/src/Symfony/Bridge/PhpUnit/Tests/Fixtures/coverage/tests/bootstrap.php
@@ -14,7 +14,7 @@ require __DIR__.'/../src/FooCov.php';
 
 require __DIR__.'/../../../../Legacy/CoverageListenerTrait.php';
 
-if (class_exists('PHPUnit_Runner_Version') && version_compare(\PHPUnit_Runner_Version::id(), '6.0.0', '<')) {
+if (version_compare(\PHPUnit\Runner\Version::id(), '6.0.0', '<')) {
     require_once __DIR__.'/../../../../Legacy/CoverageListenerForV5.php';
 } elseif (version_compare(\PHPUnit\Runner\Version::id(), '7.0.0', '<')) {
     require_once __DIR__.'/../../../../Legacy/CoverageListenerForV6.php';
diff --git a/src/Symfony/Bridge/PhpUnit/Tests/ProcessIsolationTest.php b/src/Symfony/Bridge/PhpUnit/Tests/ProcessIsolationTest.php
index b8125dc558..b4789ad1f3 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/ProcessIsolationTest.php
+++ b/src/Symfony/Bridge/PhpUnit/Tests/ProcessIsolationTest.php
@@ -24,8 +24,7 @@ class ProcessIsolationTest extends TestCase
 
     public function testCallingOtherErrorHandler()
     {
-        $class = class_exists('PHPUnit\Framework\Exception') ? 'PHPUnit\Framework\Exception' : 'PHPUnit_Framework_Exception';
-        $this->expectException($class);
+        $this->expectException(\class_exists('PHPUnit_Framework_Exception') ? 'PHPUnit_Framework_Exception' : 'PHPUnit\Framework\Exception');
         $this->expectExceptionMessage('Test that PHPUnit\'s error handler fires.');
 
         trigger_error('Test that PHPUnit\'s error handler fires.', E_USER_WARNING);
diff --git a/src/Symfony/Bridge/PhpUnit/TextUI/Command.php b/src/Symfony/Bridge/PhpUnit/TextUI/Command.php
index 4a26fc7fad..be73e4d2be 100644
--- a/src/Symfony/Bridge/PhpUnit/TextUI/Command.php
+++ b/src/Symfony/Bridge/PhpUnit/TextUI/Command.php
@@ -11,7 +11,7 @@
 
 namespace Symfony\Bridge\PhpUnit\TextUI;
 
-if (class_exists('PHPUnit_Runner_Version') && version_compare(\PHPUnit_Runner_Version::id(), '6.0.0', '<')) {
+if (version_compare(\PHPUnit\Runner\Version::id(), '6.0.0', '<')) {
     class_alias('Symfony\Bridge\PhpUnit\Legacy\CommandForV5', 'Symfony\Bridge\PhpUnit\TextUI\Command');
 } else {
     class_alias('Symfony\Bridge\PhpUnit\Legacy\CommandForV6', 'Symfony\Bridge\PhpUnit\TextUI\Command');
diff --git a/src/Symfony/Bridge/PhpUnit/bootstrap.php b/src/Symfony/Bridge/PhpUnit/bootstrap.php
index 5de9467891..26bde7335d 100644
--- a/src/Symfony/Bridge/PhpUnit/bootstrap.php
+++ b/src/Symfony/Bridge/PhpUnit/bootstrap.php
@@ -12,6 +12,95 @@
 use Doctrine\Common\Annotations\AnnotationRegistry;
 use Symfony\Bridge\PhpUnit\DeprecationErrorHandler;
 
+if (class_exists('PHPUnit_Runner_Version') && version_compare(\PHPUnit_Runner_Version::id(), '6.0.0', '<')) {
+    $classes = [
+        'PHPUnit_Framework_Assert', // override PhpUnit's ForwardCompat child class
+        'PHPUnit_Framework_AssertionFailedError', // override PhpUnit's ForwardCompat child class
+        'PHPUnit_Framework_BaseTestListener', // override PhpUnit's ForwardCompat child class
+
+        'PHPUnit_Framework_Constraint',
+        'PHPUnit_Framework_Constraint_And',
+        'PHPUnit_Framework_Constraint_ArrayHasKey',
+        'PHPUnit_Framework_Constraint_ArraySubset',
+        'PHPUnit_Framework_Constraint_Attribute',
+        'PHPUnit_Framework_Constraint_Callback',
+        'PHPUnit_Framework_Constraint_ClassHasAttribute',
+        'PHPUnit_Framework_Constraint_ClassHasStaticAttribute',
+        'PHPUnit_Framework_Constraint_Composite',
+        'PHPUnit_Framework_Constraint_Count',
+        'PHPUnit_Framework_Constraint_Exception',
+        'PHPUnit_Framework_Constraint_ExceptionCode',
+        'PHPUnit_Framework_Constraint_ExceptionMessage',
+        'PHPUnit_Framework_Constraint_ExceptionMessageRegExp',
+        'PHPUnit_Framework_Constraint_FileExists',
+        'PHPUnit_Framework_Constraint_GreaterThan',
+        'PHPUnit_Framework_Constraint_IsAnything',
+        'PHPUnit_Framework_Constraint_IsEmpty',
+        'PHPUnit_Framework_Constraint_IsEqual',
+        'PHPUnit_Framework_Constraint_IsFalse',
+        'PHPUnit_Framework_Constraint_IsIdentical',
+        'PHPUnit_Framework_Constraint_IsInstanceOf',
+        'PHPUnit_Framework_Constraint_IsJson',
+        'PHPUnit_Framework_Constraint_IsNull',
+        'PHPUnit_Framework_Constraint_IsTrue',
+        'PHPUnit_Framework_Constraint_IsType',
+        'PHPUnit_Framework_Constraint_JsonMatches',
+        'PHPUnit_Framework_Constraint_JsonMatches_ErrorMessageProvider',
+        'PHPUnit_Framework_Constraint_LessThan',
+        'PHPUnit_Framework_Constraint_Not',
+        'PHPUnit_Framework_Constraint_ObjectHasAttribute',
+        'PHPUnit_Framework_Constraint_Or',
+        'PHPUnit_Framework_Constraint_PCREMatch',
+        'PHPUnit_Framework_Constraint_SameSize',
+        'PHPUnit_Framework_Constraint_StringContains',
+        'PHPUnit_Framework_Constraint_StringEndsWith',
+        'PHPUnit_Framework_Constraint_StringMatches',
+        'PHPUnit_Framework_Constraint_StringStartsWith',
+        'PHPUnit_Framework_Constraint_TraversableContains',
+        'PHPUnit_Framework_Constraint_TraversableContainsOnly',
+        'PHPUnit_Framework_Constraint_Xor',
+
+        'PHPUnit_Framework_Error',
+        'PHPUnit_Framework_Error_Deprecated',
+        'PHPUnit_Framework_Error_Notice',
+        'PHPUnit_Framework_Error_Warning',
+        'PHPUnit_Framework_Exception',
+        'PHPUnit_Framework_ExpectationFailedException',
+
+        'PHPUnit_Framework_MockObject_MockObject',
+
+        'PHPUnit_Framework_IncompleteTest',
+        'PHPUnit_Framework_IncompleteTestCase',
+        'PHPUnit_Framework_IncompleteTestError',
+        'PHPUnit_Framework_RiskyTest',
+        'PHPUnit_Framework_RiskyTestError',
+        'PHPUnit_Framework_SkippedTest',
+        'PHPUnit_Framework_SkippedTestCase',
+        'PHPUnit_Framework_SkippedTestError',
+        'PHPUnit_Framework_SkippedTestSuiteError',
+
+        'PHPUnit_Framework_SyntheticError',
+
+        'PHPUnit_Framework_Test',
+        'PHPUnit_Framework_TestCase', // override PhpUnit's ForwardCompat child class
+        'PHPUnit_Framework_TestFailure',
+        'PHPUnit_Framework_TestListener',
+        'PHPUnit_Framework_TestResult',
+        'PHPUnit_Framework_TestSuite', // override PhpUnit's ForwardCompat child class
+
+        'PHPUnit_Runner_BaseTestRunner',
+        'PHPUnit_Runner_Version',
+
+        'PHPUnit_Util_Blacklist',
+        'PHPUnit_Util_ErrorHandler',
+        'PHPUnit_Util_Test',
+        'PHPUnit_Util_XML',
+    ];
+    foreach ($classes as $class) {
+        class_alias($class, '\\'.strtr($class, '_', '\\'), true);
+    }
+}
+
 // Detect if we need to serialize deprecations to a file.
 if ($file = getenv('SYMFONY_DEPRECATIONS_SERIALIZE')) {
     DeprecationErrorHandler::collectDeprecations($file);