diff -u b/core/modules/field/tests/modules/field_computed_test/field_computed_test.module b/core/modules/field/tests/modules/field_computed_test/field_computed_test.module
--- b/core/modules/field/tests/modules/field_computed_test/field_computed_test.module
+++ b/core/modules/field/tests/modules/field_computed_test/field_computed_test.module
@@ -57 +57 @@
-}
\ No newline at end of file
+}
diff -u b/core/modules/field/tests/modules/field_computed_test/src/Plugin/Field/FieldType/ComputedValuesItemList.php b/core/modules/field/tests/modules/field_computed_test/src/Plugin/Field/FieldType/ComputedValuesItemList.php
--- b/core/modules/field/tests/modules/field_computed_test/src/Plugin/Field/FieldType/ComputedValuesItemList.php
+++ b/core/modules/field/tests/modules/field_computed_test/src/Plugin/Field/FieldType/ComputedValuesItemList.php
@@ -23,40 +23,33 @@
         return $items;
-        break;
+
       case 'valid_computed_entity_reference':
         $items = [];
         $parent = $this->getEntity();
         if (!$parent->isNew()) {
           $items[] = $this->createItem(0, [
-            'target_id' => $parent->id() == 1 ? 2 : 1,
+            'target_id' => $parent->id() === 1 ? 2 : 1,
           ]);
         }
         return $items;
-        break;
+
       case 'non_valid_computed_entity_reference':
         $items = [];
         $parent = $this->getEntity();
         if (!$parent->isNew()) {
           $items[] = $this->createItem(0, [
-            'target_id' => '3', // Non existing entity reference.
+            'target_id' => '3',
           ]);
         }
         return $items;
-        break;
+
       case 'non_valid_computed_timestamp':
         $items = [];
         $items[] = $this->createItem(0, [
           'value' => 'A',
         ]);
         return $items;
-        break;
-      case 'non_valid_computed_entity_reference':
-        $items = [];
-        $items[] = $this->createItem(0, [
-          'target_id' => 3,
-        ]);
-        break;
     }
+    return [];
   }
 
-
 }
diff -u b/core/modules/field/tests/src/Kernel/FieldComputedTest.php b/core/modules/field/tests/src/Kernel/FieldComputedTest.php
--- b/core/modules/field/tests/src/Kernel/FieldComputedTest.php
+++ b/core/modules/field/tests/src/Kernel/FieldComputedTest.php
@@ -1,12 +1,11 @@
 <?php
 
-
 namespace Drupal\Tests\field\Kernel;
 
+use Drupal\Core\Field\FieldException;
 use Drupal\entity_test\Entity\EntityTest;
 use Drupal\KernelTests\KernelTestBase;
 
-
 /**
  * Test related to computed entity fields.
  *
@@ -29,7 +28,9 @@
   ];
 
   /**
-   * @var EntityTest[]
+   * A list of entities to test.
+   *
+   * @var \Drupal\entity_test\Entity\EntityTest[]
    */
   public $entities = [];
 
@@ -46,31 +47,32 @@
    * Test a valid computed entityreference field.
    */
   public function testValidComputedEntityReference() {
-    $referencedEntity = $this->entities[0]->get('valid_computed_entity_reference')->entity;
-    $this->assertInstanceOf(EntityTest::class, $referencedEntity);
-    $this->assertEquals($this->entities[1]->id(), $referencedEntity->id());
+    /** @var \Drupal\Core\Entity\EntityInterface $referenced_entity */
+    $referenced_entity = $this->entities[0]->get('valid_computed_entity_reference')->entity;
+    $this->assertInstanceOf(EntityTest::class, $referenced_entity);
+    $this->assertEquals($this->entities[1]->id(), $referenced_entity->id());
   }
 
   /**
    * Test that a non existing entity reference returns NULL.
    */
-  public function testNonValidComputedEntityReference(){
-    $referencedEntity = $this->entities[0]->get('non_valid_computed_entity_reference')->entity;
-    $this->assertNull($referencedEntity);
+  public function testNonValidComputedEntityReference() {
+    $referenced_entity = $this->entities[0]->get('non_valid_computed_entity_reference')->entity;
+    $this->assertNull($referenced_entity);
   }
 
   /**
-   * @expectedException \Drupal\Core\Field\FieldException
-   * @expectedExceptionMessage This value should be a valid number.
+   * Test that a non valid computed timestamp returns throws an exception.
    */
   public function testNonValidComputedTimestamp() {
-    $data = [
+    $this->setExpectedException(FieldException::class, 'This value should be a valid number.');
+    $entities_data = [
       [
         'type' => 'non_valid_computed_timestamp',
         'title' => 'Entity with a non valid computed timestamp',
       ],
     ];
-    $this->createTestEntities($data);
+    $this->createTestEntities($entities_data);
   }
 
   /**
@@ -83,22 +85,23 @@
     $this->installEntitySchema('entity_test');
     $this->installEntitySchema('user');
 
-    $data = $this->getTestDataForEntities($this->getName());
-
-    $this->createTestEntities($data);
+    $entities_data = $this->getTestDataForEntities($this->getName());
+    $this->createTestEntities($entities_data);
   }
 
   /**
    * Get an array of test data for the creation of entities.
    *
-   * @param $methodName
+   * @param string $method_name
+   *   The name of the method to test.
    *
-   * @return array Data for creation of test entities.
+   * @return array
+   *   Data for creation of test entities.
    */
-  private function getTestDataForEntities($methodName){
+  protected function getTestDataForEntities($method_name) {
     $data = [];
-    switch ($methodName) {
-      case "testValidComputedTimestamp":
+    switch ($method_name) {
+      case 'testValidComputedTimestamp':
         $data = [
           [
             'type' => 'valid_computed_timestamp',
@@ -106,7 +109,8 @@
           ],
         ];
         break;
-      case "testNonValidComputedEntityReference":
+
+      case 'testNonValidComputedEntityReference':
         $data = [
           [
             'type' => 'non_valid_computed_entity_reference',
@@ -118,7 +122,8 @@
           ],
         ];
         break;
-      case "testValidComputedEntityReference":
+
+      case 'testValidComputedEntityReference':
         $data = [
           [
             'type' => 'valid_computed_entity_reference',
@@ -133,11 +138,15 @@
     }
     return $data;
   }
+
   /**
-   * Create some Test Entities based on an array of data.
+   * Create some test entities based on an array of data.
+   *
+   * @param array $entities_data
+   *   An array containing the data to create entities from.
    */
-  private function createTestEntities($data) {
-    foreach ($data as $item) {
+  protected function createTestEntities(array $entities_data) {
+    foreach ($entities_data as $item) {
       $entity = EntityTest::create([
         'type' => $item['type'],
         'title' => $item['title'],
@@ -150 +159 @@
-}
\ No newline at end of file
+}