diff --git a/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php b/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php
index 32ec62205f1..250ea06b17d 100644
--- a/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php
@@ -187,7 +187,7 @@ EOD;
       $this->drupalPostForm(NULL, [], t('Confirm'));
       $entity = $storage->load('second');
       $this->assertRaw(t('The configuration was imported successfully.'));
-      $this->assertTrue(is_string($entity->label()), 'Entity label is a string');
+      $this->assertIsString($entity->label());
       $this->assertStringContainsString('ObjectSerialization', $entity->label(), 'Label contains serialized object');
     }
     else {
diff --git a/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php b/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php
index bb8187cc9e1..1b4ae129cc0 100644
--- a/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php
@@ -53,7 +53,7 @@ class ThemeTokenTest extends BrowserTestBase {
     $settings = $this->getDrupalSettings();
     $this->assertNotNull($settings['ajaxPageState']['theme_token']);
     // The CSRF token is a 43 length string.
-    $this->assertTrue(is_string($settings['ajaxPageState']['theme_token']));
+    $this->assertIsString($settings['ajaxPageState']['theme_token']);
     $this->assertEqual(strlen($settings['ajaxPageState']['theme_token']), 43);
   }
 
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php b/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php
index 58d6bb309c4..ebec18d7086 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php
@@ -390,7 +390,7 @@ class EntityFieldTest extends EntityKernelTestBase {
 
     // Access the name field.
     $this->assertEqual(1, $entity->id->value, new FormattableMarkup('%entity_type: ID value can be read.', ['%entity_type' => $entity_type]));
-    $this->assertTrue(is_string($entity->uuid->value), new FormattableMarkup('%entity_type: UUID value can be read.', ['%entity_type' => $entity_type]));
+    $this->assertIsString($entity->uuid->value);
     $this->assertEqual('en', $entity->{$langcode_key}->value, new FormattableMarkup('%entity_type: Language code can be read.', ['%entity_type' => $entity_type]));
     $this->assertEqual(\Drupal::languageManager()->getLanguage('en'), $entity->{$langcode_key}->language, new FormattableMarkup('%entity_type: Language object can be read.', ['%entity_type' => $entity_type]));
     $this->assertEqual($this->entityUser->id(), $entity->user_id->target_id, new FormattableMarkup('%entity_type: User id can be read.', ['%entity_type' => $entity_type]));
diff --git a/core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php b/core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php
index a7b21349409..c164e5fb7fd 100644
--- a/core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php
+++ b/core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php
@@ -73,7 +73,7 @@ class TypedDataTest extends KernelTestBase {
     $typed_data->setValue(FALSE);
     $this->assertTrue($typed_data->getValue() === FALSE, 'Boolean value was changed.');
     $this->assertEqual($typed_data->validate()->count(), 0);
-    $this->assertTrue(is_string($typed_data->getString()), 'Boolean value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'Boolean wrapper is null-able.');
     $this->assertEqual($typed_data->validate()->count(), 0);
@@ -91,7 +91,7 @@ class TypedDataTest extends KernelTestBase {
     $this->assertTrue($typed_data->getValue() === $new_value, 'String value was changed.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     // Funky test.
-    $this->assertTrue(is_string($typed_data->getString()), 'String value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'String wrapper is null-able.');
     $this->assertEqual($typed_data->validate()->count(), 0);
@@ -107,7 +107,7 @@ class TypedDataTest extends KernelTestBase {
     $new_value = rand();
     $typed_data->setValue($new_value);
     $this->assertTrue($typed_data->getValue() === $new_value, 'Integer value was changed.');
-    $this->assertTrue(is_string($typed_data->getString()), 'Integer value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'Integer wrapper is null-able.');
@@ -124,7 +124,7 @@ class TypedDataTest extends KernelTestBase {
     $new_value = 678.90;
     $typed_data->setValue($new_value);
     $this->assertTrue($typed_data->getValue() === $new_value, 'Float value was changed.');
-    $this->assertTrue(is_string($typed_data->getString()), 'Float value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'Float wrapper is null-able.');
@@ -229,7 +229,7 @@ class TypedDataTest extends KernelTestBase {
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue('P40D');
     $this->assertEqual($typed_data->getDuration()->d, 40, 'DurationIso8601 value was changed and set by duration string.');
-    $this->assertTrue(is_string($typed_data->getString()), 'DurationIso8601 value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'DurationIso8601 wrapper is null-able.');
@@ -253,7 +253,7 @@ class TypedDataTest extends KernelTestBase {
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(60 * 60 * 4);
     $this->assertEqual($typed_data->getDuration()->s, 14400, 'Time span was changed');
-    $this->assertTrue(is_string($typed_data->getString()), 'Time span value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'Time span wrapper is null-able.');
@@ -276,7 +276,7 @@ class TypedDataTest extends KernelTestBase {
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue($uri . 'bar.txt');
     $this->assertTrue($typed_data->getValue() === $uri . 'bar.txt', 'URI value was changed.');
-    $this->assertTrue(is_string($typed_data->getString()), 'URI value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'URI wrapper is null-able.');
@@ -304,7 +304,7 @@ class TypedDataTest extends KernelTestBase {
     $new_value = 'test@example.com';
     $typed_data->setValue($new_value);
     $this->assertIdentical($typed_data->getValue(), $new_value, 'Email value was changed.');
-    $this->assertTrue(is_string($typed_data->getString()), 'Email value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'Email wrapper is null-able.');
@@ -320,12 +320,12 @@ class TypedDataTest extends KernelTestBase {
     // Try setting by URI.
     $typed_data->setValue($files[1]->getFileUri());
     $this->assertEqual(fgets($typed_data->getValue()), fgets(fopen($files[1]->getFileUri(), 'r')), 'Binary value was changed.');
-    $this->assertTrue(is_string($typed_data->getString()), 'Binary value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     // Try setting by resource.
     $typed_data->setValue(fopen($files[2]->getFileUri(), 'r'));
     $this->assertEqual(fgets($typed_data->getValue()), fgets(fopen($files[2]->getFileUri(), 'r')), 'Binary value was changed.');
-    $this->assertTrue(is_string($typed_data->getString()), 'Binary value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'Binary wrapper is null-able.');
@@ -340,7 +340,7 @@ class TypedDataTest extends KernelTestBase {
     $new_value = 'test@example.com';
     $typed_data->setValue($new_value);
     $this->assertIdentical($typed_data->getValue(), $new_value, 'Any value was changed.');
-    $this->assertTrue(is_string($typed_data->getString()), 'Any value was converted to string');
+    $this->assertIsString($typed_data->getString());
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getValue(), 'Any wrapper is null-able.');