diff --git a/core/tests/Drupal/Tests/Phpunit4CompatibilityTest.php b/core/tests/Drupal/Tests/Phpunit4CompatibilityTest.php
deleted file mode 100644
index 639e6fa35f3e8ae7b24ed6cbb8717bede81866bf..0000000000000000000000000000000000000000
--- a/core/tests/Drupal/Tests/Phpunit4CompatibilityTest.php
+++ /dev/null
@@ -1,89 +0,0 @@
-<?php
-
-namespace Drupal\Tests;
-
-/**
- * Tests existence of the PHPUnit4 backward compatibility classes.
- *
- * @group Tests
- */
-class Phpunit4CompatibilityTest extends UnitTestCase {
-
-  /**
-   * Tests existence of \PHPUnit_Framework_AssertionFailedError.
-   */
-  public function testFrameworkAssertionFailedError() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_AssertionFailedError'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_Constraint_Count.
-   */
-  public function testFrameworkConstraintCount() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_Constraint_Count'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_Error.
-   */
-  public function testFrameworkError() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_Error'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_Error_Warning.
-   */
-  public function FrameworkErrorWarning() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_Error_Warning'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_Exception.
-   */
-  public function testFrameworkException() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_Exception'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_ExpectationFailedException.
-   */
-  public function testFrameworkExpectationFailedException() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_ExpectationFailedException'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_MockObject_Matcher_InvokedRecorder.
-   */
-  public function testFrameworkMockObjectMatcherInvokedRecorder() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_MockObject_Matcher_InvokedRecorder'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_SkippedTestError.
-   */
-  public function testFrameworkSkippedTestError() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_SkippedTestError'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Framework_TestCase.
-   */
-  public function testFrameworkTestCase() {
-    $this->assertTrue(class_exists('\PHPUnit_Framework_TestCase'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Util_Test.
-   */
-  public function testUtilTest() {
-    $this->assertTrue(class_exists('\PHPUnit_Util_Test'));
-  }
-
-  /**
-   * Tests existence of \PHPUnit_Util_XML.
-   */
-  public function testUtilXml() {
-    $this->assertTrue(class_exists('\PHPUnit_Util_XML'));
-  }
-
-}
diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index 467e6af6e603900cbcfe87e3ed54c19c63b1855a..4146f999a75e5cba42ee7d1820da41c0e2d09bc7 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -8,17 +8,6 @@
  */
 
 use Drupal\Component\Assertion\Handle;
-use PHPUnit\Framework\AssertionFailedError;
-use PHPUnit\Framework\Constraint\Count;
-use PHPUnit\Framework\Error\Error;
-use PHPUnit\Framework\Error\Warning;
-use PHPUnit\Framework\ExpectationFailedException;
-use PHPUnit\Framework\Exception;
-use PHPUnit\Framework\MockObject\Matcher\InvokedRecorder;
-use PHPUnit\Framework\SkippedTestError;
-use PHPUnit\Framework\TestCase;
-use PHPUnit\Util\Test;
-use PHPUnit\Util\Xml;
 
 /**
  * Finds all valid extension directories recursively within a given directory.
@@ -184,18 +173,3 @@ function drupal_phpunit_populate_class_loader() {
 // thrown if an assert fails, but this call does not turn runtime assertions on
 // if they weren't on already.
 Handle::register();
-
-// PHPUnit 4 to PHPUnit 6 bridge. Tests written for PHPUnit 4 need to work on
-// PHPUnit 6 with a minimum of fuss.
-// @todo provided for BC; remove in Drupal 9.
-class_alias(AssertionFailedError::class, '\PHPUnit_Framework_AssertionFailedError');
-class_alias(Count::class, '\PHPUnit_Framework_Constraint_Count');
-class_alias(Error::class, '\PHPUnit_Framework_Error');
-class_alias(Warning::class, '\PHPUnit_Framework_Error_Warning');
-class_alias(ExpectationFailedException::class, '\PHPUnit_Framework_ExpectationFailedException');
-class_alias(Exception::class, '\PHPUnit_Framework_Exception');
-class_alias(InvokedRecorder::class, '\PHPUnit_Framework_MockObject_Matcher_InvokedRecorder');
-class_alias(SkippedTestError::class, '\PHPUnit_Framework_SkippedTestError');
-class_alias(TestCase::class, '\PHPUnit_Framework_TestCase');
-class_alias(Test::class, '\PHPUnit_Util_Test');
-class_alias(Xml::class, '\PHPUnit_Util_XML');