diff --git a/core/lib/Drupal/Core/Test/EnvironmentCleaner.php b/core/lib/Drupal/Core/Test/EnvironmentCleaner.php
index 1785359dbb..022451669a 100644
--- a/core/lib/Drupal/Core/Test/EnvironmentCleaner.php
+++ b/core/lib/Drupal/Core/Test/EnvironmentCleaner.php
@@ -94,7 +94,8 @@ public function cleanEnvironment($clear_results = TRUE, $clear_temp_directories
    * {@inheritdoc}
    */
   public function cleanDatabase() {
-    if ($this->doCleanDatabase() > 0) {
+    $count = $this->doCleanDatabase();
+    if ($count > 0) {
       $this->output->write('Leftover tables removed: ' . $count);
     }
     else {
diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 0ef7feb12e..df35d9ee3d 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -678,11 +678,14 @@ function simpletest_generate_file($filename, $width, $lines, $type = 'binary-tex
 /**
  * Removes all temporary database tables and directories.
  *
- * @deprecated in Drupal 8.8.x and will be removed before Drupal 9.0.0. Use
+ * @deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the
+ *   environment_cleaner service and call its cleanEnvironment() method, or use
  *   \Drupal\Core\Test\EnvironmentCleaner::cleanEnvironment() instead.
+ *
+ * @see https://www.drupal.org/node/3076634
  */
 function simpletest_clean_environment() {
-  @trigger_error(__FUNCTION__, E_USER_DEPRECATED);
+  @trigger_error(__FUNCTION__ . ' is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanEnvironment() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanEnvironment() instead.. See https://www.drupal.org/node/3076634', E_USER_DEPRECATED);
   /* @var $cleaner \Drupal\simpletest\EnvironmentCleanerService */
   $cleaner = \Drupal::service('environment_cleaner');
   $cleaner->cleanEnvironment();
@@ -691,11 +694,14 @@ function simpletest_clean_environment() {
 /**
  * Removes prefixed tables from the database from crashed tests.
  *
- * @deprecated in Drupal 8.8.x and will be removed before Drupal 9.0.0. Use
+ * @deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the
+ *   environment_cleaner service and call its cleanDatabase() method, or use
  *   \Drupal\Core\Test\EnvironmentCleaner::cleanDatabase() instead.
+ *
+ * @see https://www.drupal.org/node/3076634
  */
 function simpletest_clean_database() {
-  @trigger_error(__FUNCTION__, E_USER_DEPRECATED);
+  @trigger_error(__FUNCTION__ . ' is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanDatabase() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanDatabase() instead. See https://www.drupal.org/node/3076634', E_USER_DEPRECATED);
   /* @var $cleaner \Drupal\simpletest\EnvironmentCleanerService */
   $cleaner = \Drupal::service('environment_cleaner');
   $cleaner->cleanDatabase();
@@ -704,11 +710,15 @@ function simpletest_clean_database() {
 /**
  * Finds all leftover temporary directories and removes them.
  *
- * @deprecated in Drupal 8.8.x and will be removed before Drupal 9.0.0. Use
+ * @deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the
+ *   environment_cleaner service and call its cleanTemporaryDirectories()
+ *   method, or use
  *   \Drupal\Core\Test\EnvironmentCleaner::cleanTemporaryDirectories() instead.
+ *
+ * @see https://www.drupal.org/node/3076634
  */
 function simpletest_clean_temporary_directories() {
-  @trigger_error(__FUNCTION__, E_USER_DEPRECATED);
+  @trigger_error(__FUNCTION__ . ' is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanTemporaryDirectories() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanTemporaryDirectories() instead. See https://www.drupal.org/node/3076634', E_USER_DEPRECATED);
   /* @var $cleaner \Drupal\simpletest\EnvironmentCleanerService */
   $cleaner = \Drupal::service('environment_cleaner');
   $cleaner->cleanTemporaryDirectories();
@@ -723,11 +733,14 @@ function simpletest_clean_temporary_directories() {
  * @return int
  *   The number of results that were removed.
  *
- * @deprecated in Drupal 8.8.x and will be removed before Drupal 9.0.0. Use
+ * @deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the
+ *   environment_cleaner service and call its cleanResultsTable() method, or use
  *   \Drupal\Core\Test\EnvironmentCleaner::cleanResultsTable() instead.
+ *
+ * @see https://www.drupal.org/node/3076634
  */
 function simpletest_clean_results_table($test_id = NULL) {
-  @trigger_error(__FUNCTION__, E_USER_DEPRECATED);
+  @trigger_error(__FUNCTION__ . ' is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanResultsTable() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanResultsTable() instead. See https://www.drupal.org/node/3076634', E_USER_DEPRECATED);
   if (\Drupal::config('simpletest.settings')->get('clear_results')) {
     /* @var $cleaner \Drupal\simpletest\EnvironmentCleanerService */
     $cleaner = \Drupal::service('environment_cleaner');
diff --git a/core/modules/simpletest/simpletest.services.yml b/core/modules/simpletest/simpletest.services.yml
index 85fda43284..cede4646b5 100644
--- a/core/modules/simpletest/simpletest.services.yml
+++ b/core/modules/simpletest/simpletest.services.yml
@@ -1,7 +1,7 @@
 services:
   test_discovery:
-    # @todo Change this service so that it uses \Drupal\Core\Test\TestDiscovery
-    # in https://www.drupal.org/node/1667822
+    # Drupal\simpletest\TestDiscovery is deprecated, but we still want to use it
+    # as the service here to support BC hooks.
     class: Drupal\simpletest\TestDiscovery
     arguments: ['@app.root', '@class_loader', '@module_handler']
 
diff --git a/core/modules/simpletest/tests/src/Kernel/DeprecatedCleanupTest.php b/core/modules/simpletest/tests/src/Kernel/DeprecatedCleanupTest.php
new file mode 100644
index 0000000000..a5efa34a1e
--- /dev/null
+++ b/core/modules/simpletest/tests/src/Kernel/DeprecatedCleanupTest.php
@@ -0,0 +1,65 @@
+<?php
+
+namespace Drupal\Tests\simpletest\Kernel;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Test\EnvironmentCleanerInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Symfony\Component\DependencyInjection\Definition;
+
+/**
+ * Verify deprecation errors for the cleanup functions.
+ *
+ * @group simpletest
+ * @group legacy
+ */
+class DeprecatedCleanupTest extends KernelTestBase {
+
+  public static $modules = ['simpletest'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function register(ContainerBuilder $container) {
+    parent::register($container);
+    $cleaner_definition = new Definition(StubEnvironmentCleanerService::class);
+    $container->setDefinition('environment_cleaner', $cleaner_definition);
+  }
+
+  /**
+   * @expectedDeprecation simpletest_clean_environment is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanEnvironment() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanEnvironment() instead.. See https://www.drupal.org/node/3076634
+   * @expectedDeprecation simpletest_clean_database is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanDatabase() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanDatabase() instead. See https://www.drupal.org/node/3076634
+   * @expectedDeprecation simpletest_clean_temporary_directories is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanTemporaryDirectories() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanTemporaryDirectories() instead. See https://www.drupal.org/node/3076634
+   * @expectedDeprecation simpletest_clean_results_table is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Access the environment_cleaner service and call its cleanResultsTable() method, or use \Drupal\Core\Test\EnvironmentCleaner::cleanResultsTable() instead. See https://www.drupal.org/node/3076634
+   */
+  public function testDeprecatedCleanFunctions() {
+    $this->assertNull(simpletest_clean_environment());
+    $this->assertNull(simpletest_clean_database());
+    $this->assertNull(simpletest_clean_temporary_directories());
+    $this->assertNull(simpletest_clean_results_table());
+  }
+
+}
+
+/**
+ * Mock environment_cleaner service that does not perform any cleaning.
+ */
+class StubEnvironmentCleanerService implements EnvironmentCleanerInterface {
+
+  public function cleanDatabase() {
+
+  }
+
+  public function cleanEnvironment($clear_results = TRUE, $clear_temp_directories = TRUE, $clear_database = TRUE) {
+
+  }
+
+  public function cleanResultsTable($test_id = NULL) {
+
+  }
+
+  public function cleanTemporaryDirectories() {
+
+  }
+
+}
diff --git a/core/tests/Drupal/KernelTests/Core/Test/EnvironmentCleanerTest.php b/core/tests/Drupal/KernelTests/Core/Test/EnvironmentCleanerTest.php
new file mode 100644
index 0000000000..0ca6692600
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Test/EnvironmentCleanerTest.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Test;
+
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Test\EnvironmentCleaner;
+use Drupal\KernelTests\KernelTestBase;
+use org\bovigo\vfs\vfsStream;
+use Symfony\Component\Console\Output\NullOutput;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Test\EnvironmentCleaner
+ * @group Test
+ */
+class EnvironmentCleanerTest extends KernelTestBase {
+
+  /**
+   * @covers ::doCleanTemporaryDirectories
+   */
+  public function testDoCleanTemporaryDirectories() {
+    vfsStream::setup('cleanup_test', NULL, [
+      'sites' => [
+        'simpletest' => [
+          'delete_dir' => [
+            'delete.me' => 'I am a gonner.',
+          ],
+          'delete_me.too' => 'delete this file.',
+        ],
+      ],
+    ]);
+
+    $connection = $this->prophesize(Connection::class);
+
+    $cleaner = new EnvironmentCleaner(
+      vfsStream::url('cleanup_test'),
+      $connection->reveal(),
+      $connection->reveal(),
+      new NullOutput(),
+      \Drupal::service('file_system')
+    );
+
+    $do_cleanup_ref = new \ReflectionMethod($cleaner, 'doCleanTemporaryDirectories');
+    $do_cleanup_ref->setAccessible(TRUE);
+
+    $this->assertFileExists(vfsStream::url('cleanup_test/sites/simpletest/delete_dir/delete.me'));
+    $this->assertFileExists(vfsStream::url('cleanup_test/sites/simpletest/delete_me.too'));
+
+    $this->assertEquals(2, $do_cleanup_ref->invoke($cleaner));
+
+    $this->assertDirectoryNotExists(vfsStream::url('cleanup_test/sites/simpletest/delete_dir'));
+    $this->assertFileNotExists(vfsStream::url('cleanup_test/sites/simpletest/delete_dir/delete.me'));
+    $this->assertFileNotExists(vfsStream::url('cleanup_test/sites/simpletest/delete_me.too'));
+  }
+
+}