diff --git a/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php b/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
index 8eec2cf8a4..689384e57d 100644
--- a/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
+++ b/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
@@ -142,9 +142,6 @@ public static function getSkippedDeprecations() {
     return [
       // The following deprecation message is skipped for testing purposes.
       '\Drupal\Tests\SkippedDeprecationTest deprecation',
-      // The following is a test PHPUnit deprecation warning re-thrown as a
-      // deprecation.
-      'Skipped warning for \\Drupal\\Tests\\Traits\\PHPUnit8Warnings::$deprecationWarnings',
       // The following are PHPUnit 8 deprecations that need to be resolved prior
       // to PHPUnit 9 compatibility.
       'expectExceptionMessageRegExp() is deprecated in PHPUnit 8 and will be removed in PHPUnit 9.',
diff --git a/core/tests/Drupal/Tests/PhpUnit8WarningsTest.php b/core/tests/Drupal/Tests/PhpUnit8WarningsTest.php
new file mode 100644
index 0000000000..8b83322ce2
--- /dev/null
+++ b/core/tests/Drupal/Tests/PhpUnit8WarningsTest.php
@@ -0,0 +1,74 @@
+<?php
+
+namespace Drupal\Tests;
+
+/**
+ * @group legacy
+ */
+class PhpUnit8WarningsTest extends UnitTestCase {
+
+  /**
+   * @expectedDeprecation Using assertContains() with string haystacks is deprecated and will not be supported in PHPUnit 9. Refactor your test to use assertStringContainsString() or assertStringContainsStringIgnoringCase() instead.
+   * @expectedDeprecation The optional $ignoreCase parameter of assertContains() is deprecated and will be removed in PHPUnit 9.
+   */
+  public function testAssertContains() {
+    $this->assertContains('string', 'aaaastringaaa');
+    $this->assertContains('STRING', 'aaaastringaaa', '', TRUE);
+  }
+
+  /**
+   * @expectedDeprecation Using assertNotContains() with string haystacks is deprecated and will not be supported in PHPUnit 9. Refactor your test to use assertStringNotContainsString() or assertStringNotContainsStringIgnoringCase() instead.
+   * @expectedDeprecation The optional $ignoreCase parameter of assertNotContains() is deprecated and will be removed in PHPUnit 9.
+   */
+  public function testAssertNotContains() {
+    $this->assertNotContains('foo', 'bar');
+    $this->assertNotContains('FOO', 'bar', '', TRUE);
+  }
+
+  /**
+   * @expectedDeprecation assertArraySubset() is deprecated and will be removed in PHPUnit 9.
+   */
+  public function testAssertArraySubset() {
+    $this->assertArraySubset(['a'], ['a', 'b']);
+  }
+
+  /**
+   * @expectedDeprecation assertInternalType() is deprecated and will be removed in PHPUnit 9. Refactor your test to use assertIsArray(), assertIsBool(), assertIsFloat(), assertIsInt(), assertIsNumeric(), assertIsObject(), assertIsResource(), assertIsString(), assertIsScalar(), assertIsCallable(), or assertIsIterable() instead.
+   */
+  public function testAssertInternalType() {
+    $this->assertInternalType('string', 'string');
+  }
+
+  /**
+   * @expectedDeprecation assertAttributeEquals() is deprecated and will be removed in PHPUnit 9.
+   * @expectedDeprecation readAttribute() is deprecated and will be removed in PHPUnit 9.
+   * @expectedDeprecation getObjectAttribute() is deprecated and will be removed in PHPUnit 9.
+   * @expectedDeprecation assertAttributeSame() is deprecated and will be removed in PHPUnit 9.
+   * @expectedDeprecation assertAttributeInstanceOf() is deprecated and will be removed in PHPUnit 9.
+   * @expectedDeprecation assertAttributeEmpty() is deprecated and will be removed in PHPUnit 9.
+   */
+  public function testAssertAttribute() {
+    $obj = new class() {
+      protected $attribute = 'value';
+      protected $class;
+      protected $empty;
+
+      public function __construct() {
+        $this->class = new \stdClass();
+      }
+
+    };
+    $this->assertAttributeEquals('value', 'attribute', $obj);
+    $this->assertAttributeSame('value', 'attribute', $obj);
+    $this->assertAttributeInstanceOf(\stdClass::class, 'class', $obj);
+    $this->assertAttributeEmpty('empty', $obj);
+  }
+
+  /**
+   * @expectedDeprecation The optional $canonicalize parameter of assertEquals() is deprecated and will be removed in PHPUnit 9. Refactor your test to use assertEqualsCanonicalizing() instead.
+   */
+  public function testAssertEquals() {
+    $this->assertEquals(['a', 'b'], ['b', 'a'], '', 0.0, 10, TRUE);
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/SkippedDeprecationTest.php b/core/tests/Drupal/Tests/SkippedDeprecationTest.php
index 65178df95c..b65bdd22e3 100644
--- a/core/tests/Drupal/Tests/SkippedDeprecationTest.php
+++ b/core/tests/Drupal/Tests/SkippedDeprecationTest.php
@@ -14,7 +14,6 @@ class SkippedDeprecationTest extends UnitTestCase {
    */
   public function testSkippingDeprecations() {
     @trigger_error('\Drupal\Tests\SkippedDeprecationTest deprecation', E_USER_DEPRECATED);
-    $this->addWarning('Skipped warning for \\Drupal\\Tests\\Traits\\PHPUnit8Warnings::$deprecationWarnings');
     $this->addToAssertionCount(1);
   }
 
@@ -25,7 +24,6 @@ public function testSkippingDeprecations() {
    */
   public function testSkippingDeprecationsAgain() {
     @trigger_error('\Drupal\Tests\SkippedDeprecationTest deprecation', E_USER_DEPRECATED);
-    $this->addWarning('Skipped warning for \\Drupal\\Tests\\Traits\\PHPUnit8Warnings::$deprecationWarnings');
     $this->addToAssertionCount(1);
   }
 
diff --git a/core/tests/Drupal/Tests/Traits/PHPUnit8Warnings.php b/core/tests/Drupal/Tests/Traits/PHPUnit8Warnings.php
index 3efe66c401..55a6b60504 100644
--- a/core/tests/Drupal/Tests/Traits/PHPUnit8Warnings.php
+++ b/core/tests/Drupal/Tests/Traits/PHPUnit8Warnings.php
@@ -40,9 +40,6 @@ trait PHPUnit8Warnings {
     'The optional $ignoreCase parameter of assertContains() is deprecated and will be removed in PHPUnit 9.',
     'The optional $ignoreCase parameter of assertNotContains() is deprecated and will be removed in PHPUnit 9.',
     'expectExceptionMessageRegExp() is deprecated in PHPUnit 8 and will be removed in PHPUnit 9.',
-    // Warnings for testing.
-    'Skipped warning for \\Drupal\\Tests\\Traits\\PHPUnit8Warnings::$deprecationWarnings',
-    'Un-skipped warning for \\Drupal\\Tests\\Traits\\PHPUnit8Warnings::$deprecationWarnings',
   ];
 
   /**