diff --git a/automatic_updates.services.yml b/automatic_updates.services.yml
index 45652a55de6a0f7a7be56c8eff464c7ae91ad056..c5638b40d3f98ed5095557e7da7ad8fb0ae887c8 100644
--- a/automatic_updates.services.yml
+++ b/automatic_updates.services.yml
@@ -4,32 +4,32 @@ services:
     arguments: ['@keyvalue.expirable', '@datetime.time', 24]
   automatic_updates.updater:
     class: Drupal\automatic_updates\Updater
-    arguments: [ '@state', '@string_translation','@automatic_updates.beginner', '@automatic_updates.stager', '@automatic_updates.cleaner', '@automatic_updates.committer' , '@file_system', '@event_dispatcher']
+    arguments: ['@state', '@string_translation','@automatic_updates.beginner', '@automatic_updates.stager', '@automatic_updates.cleaner', '@automatic_updates.committer' , '@file_system', '@event_dispatcher']
   automatic_updates.staged_package_validator:
     class: Drupal\automatic_updates\Validation\StagedProjectsValidation
-    arguments: [ '@string_translation', '@automatic_updates.updater' ]
+    arguments: ['@string_translation', '@automatic_updates.updater' ]
     tags:
       - { name: event_subscriber }
   automatic_updates.beginner:
     class: Drupal\automatic_updates\ComposerStager\Beginner
     arguments:
-      [ '@automatic_updates.file_copier', '@automatic_updates.file_system' ]
+      ['@automatic_updates.file_copier', '@automatic_updates.file_system' ]
   automatic_updates.stager:
     class: PhpTuf\ComposerStager\Domain\Stager
     arguments:
-      [ '@automatic_updates.composer_runner', '@automatic_updates.file_system' ]
+      ['@automatic_updates.composer_runner', '@automatic_updates.file_system' ]
   automatic_updates.cleaner:
     class: PhpTuf\ComposerStager\Domain\Cleaner
     arguments:
-      [ '@automatic_updates.file_system' ]
+      ['@automatic_updates.file_system' ]
   automatic_updates.committer:
     class: PhpTuf\ComposerStager\Domain\Committer
     arguments:
-      [ '@automatic_updates.file_copier', '@automatic_updates.file_system' ]
+      ['@automatic_updates.file_copier', '@automatic_updates.file_system' ]
   automatic_updates.composer_runner:
     class: PhpTuf\ComposerStager\Infrastructure\Process\Runner\ComposerRunner
     arguments:
-      [ '@automatic_updates.exec_finder', '@automatic_updates.process_factory' ]
+      ['@automatic_updates.exec_finder', '@automatic_updates.process_factory' ]
   automatic_updates.file_copier.factory:
     class: PhpTuf\ComposerStager\Infrastructure\Process\FileCopier\FileCopierFactory
     arguments:
@@ -55,7 +55,7 @@ services:
   automatic_updates.file_system:
     class: PhpTuf\ComposerStager\Infrastructure\Filesystem\Filesystem
     arguments:
-      [ '@automatic_updates.symfony_file_system' ]
+      ['@automatic_updates.symfony_file_system' ]
   automatic_updates.symfony_file_system:
     class: Symfony\Component\Filesystem\Filesystem
   automatic_updates.symfony_exec_finder:
@@ -63,10 +63,10 @@ services:
   automatic_updates.rsync:
     class: PhpTuf\ComposerStager\Infrastructure\Process\Runner\RsyncRunner
     arguments:
-      [ '@automatic_updates.exec_finder', '@automatic_updates.process_factory' ]
+      ['@automatic_updates.exec_finder', '@automatic_updates.process_factory' ]
   automatic_updates.exec_finder:
     class: PhpTuf\ComposerStager\Infrastructure\Process\ExecutableFinder
     arguments:
-      [ '@automatic_updates.symfony_exec_finder' ]
+      ['@automatic_updates.symfony_exec_finder' ]
   automatic_updates.process_factory:
     class: Drupal\automatic_updates\ComposerStager\ProcessFactory
diff --git a/src/BatchProcessor.php b/src/BatchProcessor.php
index 4086d2a7e1b15229e44a94411ce97110119b8318..940418929d71974983a5db8b7b305de1ca3d6411 100644
--- a/src/BatchProcessor.php
+++ b/src/BatchProcessor.php
@@ -12,7 +12,7 @@ use Symfony\Component\HttpFoundation\RedirectResponse;
 class BatchProcessor {
 
   /**
-   * Get the updater service.
+   * Gets the updater service.
    *
    * @return \Drupal\automatic_updates\Updater
    *   The updater service.
diff --git a/src/Form/UpdateReady.php b/src/Form/UpdateReady.php
index 619d0dd1ea1ac177ba85af2edd0b6fa317e81590..cb978f7d20ae3df62bb25f51882237bae107131b 100644
--- a/src/Form/UpdateReady.php
+++ b/src/Form/UpdateReady.php
@@ -102,7 +102,7 @@ class UpdateReady extends UpdateFormBase {
     $session = $this->getRequest()->getSession();
     // Store maintenance_mode setting so we can restore it when done.
     $session->set('maintenance_mode', $this->state->get('system.maintenance_mode'));
-    if ($form_state->getValue('maintenance_mode') == TRUE) {
+    if ($form_state->getValue('maintenance_mode') === TRUE) {
       $this->state->set('system.maintenance_mode', TRUE);
       // @todo unset after updater. After db update?
     }
diff --git a/src/Form/UpdaterForm.php b/src/Form/UpdaterForm.php
index 6dce8d146fc696f324aeb38b26956487b8cafae3..599c7257e0a9453a1e9c0a9881c217d7c2b21aca 100644
--- a/src/Form/UpdaterForm.php
+++ b/src/Form/UpdaterForm.php
@@ -99,7 +99,7 @@ class UpdaterForm extends UpdateFormBase {
     $project = $project_data['drupal'];
 
     // If we're already up-to-date, there's nothing else we need to do.
-    if ($project['status'] == UpdateManagerInterface::CURRENT) {
+    if ($project['status'] === UpdateManagerInterface::CURRENT) {
       $this->messenger()->addMessage('No update available');
       return $form;
     }
@@ -190,7 +190,7 @@ class UpdaterForm extends UpdateFormBase {
   /**
    * Builds the form actions.
    *
-   * @return array
+   * @return mixed[][]
    *   The form's actions elements.
    */
   protected function actions(): array {
diff --git a/src/Updater.php b/src/Updater.php
index 6e4b9f55c254b6fa7b73048d432b10e7581127b3..b5751a48c23450186865b1243efd4f1c4c22d37d 100644
--- a/src/Updater.php
+++ b/src/Updater.php
@@ -80,7 +80,7 @@ class Updater {
   protected $eventDispatcher;
 
   /**
-   * Updater constructor.
+   * Constructs an Updater object.
    *
    * @param \Drupal\Core\State\StateInterface $state
    *   The state service.
diff --git a/tests/modules/automatic_updates_test/src/MetadataController.php b/tests/modules/automatic_updates_test/src/MetadataController.php
index 8c8e480b0560ee4d508fc4543e8a82f46a2bf77c..c00cce391a893d75347b32b67c4118b3b53613ee 100644
--- a/tests/modules/automatic_updates_test/src/MetadataController.php
+++ b/tests/modules/automatic_updates_test/src/MetadataController.php
@@ -16,7 +16,7 @@ class MetadataController extends ControllerBase {
    * testing automatic updates. This was done in order to use a different
    * directory of mock XML files.
    */
-  public function updateTest($project_name = 'drupal', $version = NULL) {
+  public function updateTest($project_name = 'drupal', $version = NULL): Response {
     if ($project_name !== 'drupal') {
       return new Response();
     }
diff --git a/tests/src/Build/AttendedUpdateTestBase.php b/tests/src/Build/AttendedUpdateTestBase.php
index 1de9ad105c54ecf34fa06a46d1a4d4d3e814d349..9d2f2ef93a7f5e9b1d207bd6a6740b9176116820 100644
--- a/tests/src/Build/AttendedUpdateTestBase.php
+++ b/tests/src/Build/AttendedUpdateTestBase.php
@@ -118,7 +118,7 @@ END;
   /**
    * Returns the data to write to the test site's composer.json.
    *
-   * @return array
+   * @return mixed[]
    *   The data that should be written to the test site's composer.json.
    */
   protected function getComposerConfiguration(): array {
diff --git a/tests/src/Traits/JsonTrait.php b/tests/src/Traits/JsonTrait.php
index 3299ea439ff8d5b67c093329229e5d5e17b1d5e5..2c216306b2cc6b3a65e047a4b2ac6aa472612436 100644
--- a/tests/src/Traits/JsonTrait.php
+++ b/tests/src/Traits/JsonTrait.php
@@ -16,7 +16,7 @@ trait JsonTrait {
    * @param string $path
    *   The path of the file to read.
    *
-   * @return array
+   * @return mixed[]
    *   The parsed data in the file.
    */
   protected function readJson(string $path): array {
diff --git a/tests/src/Traits/LocalPackagesTrait.php b/tests/src/Traits/LocalPackagesTrait.php
index 938ca0a268edf44f10d0864dd0d5fa7e0aeb2ed2..f99b7e061cc98393a4878eedbcd3e349de3fa37b 100644
--- a/tests/src/Traits/LocalPackagesTrait.php
+++ b/tests/src/Traits/LocalPackagesTrait.php
@@ -30,7 +30,7 @@ trait LocalPackagesTrait {
    * @param string $dir
    *   The directory which contains composer.lock.
    *
-   * @return array[]
+   * @return mixed[][]
    *   The local path repositories' configuration, for inclusion in a
    *   composer.json file.
    */
@@ -67,7 +67,7 @@ trait LocalPackagesTrait {
    * @param string $dir
    *   The directory which contains the lock file.
    *
-   * @return array[]
+   * @return mixed[][]
    *   All package information (including dev packages) from the lock file.
    */
   private function getPackagesFromLockFile(string $dir): array {
diff --git a/tests/src/Unit/StagedProjectsValidationTest.php b/tests/src/Unit/StagedProjectsValidationTest.php
index c3b256bfa7d5bb1ab0c8bbfb7577f5acfbeaa238..a746e6708f9c6c63d665c279603f6e270362b8f3 100644
--- a/tests/src/Unit/StagedProjectsValidationTest.php
+++ b/tests/src/Unit/StagedProjectsValidationTest.php
@@ -119,7 +119,7 @@ class StagedProjectsValidationTest extends UnitTestCase {
    *
    * @covers ::validateStagedProjects
    */
-  public function testNoErrors() {
+  public function testNoErrors(): void {
     $fixtures_dir = realpath(__DIR__ . '/../../fixtures/project_staged_validation/no_errors');
     $updater = $this->prophesize(Updater::class);
     $updater->getActiveDirectory()->willReturn("$fixtures_dir/active");