diff --git a/core/modules/simpletest/simpletest.api.php b/core/modules/simpletest/simpletest.api.php
index ea83e07dc6..fca74230b4 100644
--- a/core/modules/simpletest/simpletest.api.php
+++ b/core/modules/simpletest/simpletest.api.php
@@ -13,8 +13,7 @@
 /**
  * Alter the list of tests.
  *
- * This hook is only invoked by the Simpletest UI builder. It will not be
- * invoked by run-tests.sh or the phpunit tool.
+ * This hook will not be invoked by the phpunit tool.
  *
  * @param $groups
  *   A two dimensional array, the first key is the test group, the second is the
diff --git a/core/modules/simpletest/tests/modules/simpletest_deprecation_test/simpletest_deprecation_test.info.yml b/core/modules/simpletest/tests/modules/simpletest_deprecation_test/simpletest_deprecation_test.info.yml
new file mode 100644
index 0000000000..2cb995bd85
--- /dev/null
+++ b/core/modules/simpletest/tests/modules/simpletest_deprecation_test/simpletest_deprecation_test.info.yml
@@ -0,0 +1,6 @@
+name: 'Simpletest deprecation test'
+type: module
+description: 'Support module for Simpletest deprecation tests.'
+package: Testing
+version: VERSION
+core: 8.x
diff --git a/core/modules/simpletest/tests/modules/simpletest_deprecation_test/simpletest_deprecation_test.module b/core/modules/simpletest/tests/modules/simpletest_deprecation_test/simpletest_deprecation_test.module
new file mode 100644
index 0000000000..f61059783c
--- /dev/null
+++ b/core/modules/simpletest/tests/modules/simpletest_deprecation_test/simpletest_deprecation_test.module
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * @file
+ * Mock module for testing simpletest.
+ */
+
+/**
+ * Implements hook_simpletest_alter().
+ *
+ * This hook is deprecated and should trigger a deprecation error when invoked.
+ */
+function simpletest_deprecation_test_simpletest_alter(&$groups) {
+  // No-op.
+}
diff --git a/core/modules/simpletest/tests/src/Kernel/TestDiscoveryDeprecationTest.php b/core/modules/simpletest/tests/src/Kernel/TestDiscoveryDeprecationTest.php
new file mode 100644
index 0000000000..984542fa26
--- /dev/null
+++ b/core/modules/simpletest/tests/src/Kernel/TestDiscoveryDeprecationTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Drupal\Tests\simpletest\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @group simpletest
+ * @group legacy
+ *
+ * @coversDefaultClass \Drupal\simpletest\TestDiscovery
+ */
+class TestDiscoveryDeprecationTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['simpletest', 'simpletest_deprecation_test'];
+
+  /**
+   * @expectedDeprecation The deprecated alter hook hook_simpletest_alter() is implemented in these functions: simpletest_deprecation_test_simpletest_alter. Convert your test to a PHPUnit-based one and implement test listeners.
+   * @covers ::getTestClasses
+   */
+  public function testHookSimpletestAlter() {
+    // The simpletest_test module implements hook_simpletest_alter(), which
+    // should trigger a deprecation error during getTestClasses().
+    $this->assertNotEmpty(
+      $this->container->get('test_discovery')->getTestClasses()
+    );
+  }
+
+}