diff --git a/core/modules/system/tests/src/Kernel/Entity/EntityReferenceSelectionReferenceableTest.php b/core/modules/system/tests/src/Kernel/Entity/EntityReferenceSelectionReferenceableTest.php
index af18be632f..21858088df 100644
--- a/core/modules/system/tests/src/Kernel/Entity/EntityReferenceSelectionReferenceableTest.php
+++ b/core/modules/system/tests/src/Kernel/Entity/EntityReferenceSelectionReferenceableTest.php
@@ -119,7 +119,7 @@ public function testReferenceablesWithNoLabelKey($match, $match_operator, $limit
       // entity labels.
       // @see \Drupal\Core\Entity\EntityReferenceSelection\SelectionInterface::getReferenceableEntities()
       $item = is_string($item) ? Html::escape($item) : $item;
-      $this->assertTrue(array_search($item, $referenceables[$this->bundle]) !== FALSE);
+      $this->assertContains($item, $referenceables[$this->bundle]);
     }
 
     // Test ::countReferenceableEntities().
diff --git a/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php b/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php
index 99953d0f3a..b31580e9a9 100644
--- a/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php
+++ b/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php
@@ -89,10 +89,10 @@ private function userLoadAndCheckRoleAssigned($account, $rid, $is_assigned = TRU
     $user_storage->resetCache([$account->id()]);
     $account = $user_storage->load($account->id());
     if ($is_assigned) {
-      $this->assertFalse(array_search($rid, $account->getRoles()) === FALSE, 'The role is present in the user object.');
+      $this->assertContains($rid, $account->getRoles());
     }
     else {
-      $this->assertTrue(array_search($rid, $account->getRoles()) === FALSE, 'The role is not present in the user object.');
+      $this->assertNotContains($rid, $account->getRoles());
     }
   }
 
diff --git a/core/modules/views_ui/tests/src/Kernel/TagTest.php b/core/modules/views_ui/tests/src/Kernel/TagTest.php
index b9846ec3b7..b6b0cee81a 100644
--- a/core/modules/views_ui/tests/src/Kernel/TagTest.php
+++ b/core/modules/views_ui/tests/src/Kernel/TagTest.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\Tests\views_ui\Kernel;
 
-use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Tests\views\Kernel\ViewsKernelTestBase;
 use Drupal\views_ui\Controller\ViewsUIController;
 use Drupal\Component\Utility\Html;
@@ -59,7 +58,7 @@ public function testViewsUiAutocompleteTag() {
     $matches = (array) json_decode($result->getContent(), TRUE);
     $this->assertEqual(count($matches), 8, 'Make sure that only a subset is returned.');
     foreach ($matches as $tag) {
-      $this->assertTrue(array_search($tag['value'], $tags) !== FALSE, new FormattableMarkup('Make sure the returned tag @tag actually exists.', ['@tag' => $tag['value']]));
+      $this->assertContains($tag['value'], $tags);
     }
 
     // Make sure an invalid result doesn't return anything.
diff --git a/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php b/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php
index 19b7aee5e7..832c9b1d81 100644
--- a/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php
+++ b/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php
@@ -139,7 +139,7 @@ public function testCompileDIC() {
     // Check that the container itself is not among the persist IDs because it
     // does not make sense to persist the container itself.
     $persist_ids = $container->getParameter('persist_ids');
-    $this->assertFalse(array_search('service_container', $persist_ids));
+    $this->assertNotContains('service_container', $persist_ids);
   }
 
   /**