diff --git a/core/modules/system/tests/modules/entity_test/src/Plugin/DataType/ComputedString.php b/core/modules/system/tests/modules/entity_test/src/Plugin/DataType/ComputedString.php
deleted file mode 100644
index a3b77aeed9..0000000000
--- a/core/modules/system/tests/modules/entity_test/src/Plugin/DataType/ComputedString.php
+++ /dev/null
@@ -1,39 +0,0 @@
-<?php
-
-namespace Drupal\entity_test\Plugin\DataType;
-
-/**
- * Computed string for testing.
- *
- * @internal
- *
- * @see \Drupal\entity_test\Plugin\DataType\ComputedStringData
- */
-class ComputedString {
-
-  /**
-   * The string value before computation.
-   *
-   * @var string
-   */
-  protected $sourceString;
-
-  /**
-   * Constructs a ComputedString object.
-   *
-   * @param string $not_computed_value
-   *   The text value before being computed.
-   */
-  public function __construct($not_computed_value) {
-    $this->sourceString = $not_computed_value;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function __toString() {
-    // Computation is simple concatenation for test.
-    return "Computed! " . $this->sourceString;
-  }
-
-}
diff --git a/core/modules/system/tests/modules/entity_test/src/Plugin/DataType/ComputedStringData.php b/core/modules/system/tests/modules/entity_test/src/Plugin/DataType/ComputedStringData.php
deleted file mode 100644
index b13d0d72c5..0000000000
--- a/core/modules/system/tests/modules/entity_test/src/Plugin/DataType/ComputedStringData.php
+++ /dev/null
@@ -1,34 +0,0 @@
-<?php
-
-namespace Drupal\entity_test\Plugin\DataType;
-
-use Drupal\Core\TypedData\Plugin\DataType\StringData;
-
-/**
- * The computed string test data type.
- *
- * @DataType(
- *   id = "computed_string_test",
- *   label = @Translation("Computed string (test)")
- * )
- */
-class ComputedStringData extends StringData {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getValue() {
-    /** @var \Drupal\Core\Field\FieldItemInterface $item */
-    $item = $this->getParent();
-    $computed = new ComputedString($item->get('value')->getString());
-    return $computed;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getCastedValue() {
-    return (string) $this->getValue();
-  }
-
-}
diff --git a/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/InternalPropertyTestFieldItem.php b/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/InternalPropertyTestFieldItem.php
index 5fa17e10e4..b981339efa 100644
--- a/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/InternalPropertyTestFieldItem.php
+++ b/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/InternalPropertyTestFieldItem.php
@@ -6,7 +6,7 @@
 use Drupal\Core\Field\Plugin\Field\FieldType\StringItem;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
 use Drupal\Core\TypedData\DataDefinition;
-use Drupal\entity_test\Plugin\DataType\ComputedStringData;
+use Drupal\entity_test\TypedData\ComputedString;
 
 /**
  * Defines the 'Internal Property' entity test field type.
@@ -29,16 +29,16 @@ public static function propertyDefinitions(FieldStorageDefinitionInterface $fiel
     $properties = parent::propertyDefinitions($field_definition);
 
     // Add a computed property that is non-internal.
-    $properties['non_internal_value'] = DataDefinition::create('computed_string_test')
+    $properties['non_internal_value'] = DataDefinition::create('string')
       ->setLabel(new TranslatableMarkup('Computed string, non-internal'))
       ->setComputed(TRUE)
-      ->setClass(ComputedStringData::class)
+      ->setClass(ComputedString::class)
       ->setInternal(FALSE);
     // Add a computed property that is internal.
-    $properties['internal_value'] = DataDefinition::create('computed_string_test')
+    $properties['internal_value'] = DataDefinition::create('string')
       ->setLabel(new TranslatableMarkup('Computed string, internal'))
       ->setComputed(TRUE)
-      ->setClass(ComputedStringData::class);
+      ->setClass(ComputedString::class);
     return $properties;
   }
 
diff --git a/core/modules/system/tests/modules/entity_test/src/TypedData/ComputedString.php b/core/modules/system/tests/modules/entity_test/src/TypedData/ComputedString.php
new file mode 100644
index 0000000000..121699c807
--- /dev/null
+++ b/core/modules/system/tests/modules/entity_test/src/TypedData/ComputedString.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace Drupal\entity_test\TypedData;
+
+use Drupal\Core\TypedData\TypedData;
+
+/**
+ * A computed property for test strings.
+ */
+class ComputedString extends TypedData {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getValue() {
+    /** @var \Drupal\Core\Field\FieldItemInterface $item */
+    $item = $this->getParent();
+    $computed_value = "Computed! " . $item->get('value')->getString();
+
+    return $computed_value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCastedValue() {
+    return $this->getString();
+  }
+
+}