diff --git a/core/modules/datetime/src/Tests/DateTestBase.php b/core/modules/datetime/src/Tests/DateTestBase.php
index 5c476a0..07e1d0e 100644
--- a/core/modules/datetime/src/Tests/DateTestBase.php
+++ b/core/modules/datetime/src/Tests/DateTestBase.php
@@ -196,9 +196,8 @@ protected function setSiteTimezone($timezone) {
    */
   protected function massageTestDate($date) {
     if ($this->field->getSetting('datetime_type') === DateTimeItem::DATETIME_TYPE_DATE) {
-      // Mirror what \Drupal\datetime\DateTimeComputed::getValue() does to
-      // date-only items.
-      $date->setTime(12, 0, 0);
+      // Set the default time for date-only items.
+      DateTimeItem::setDefaultDateTime($date);
     }
   }
 
diff --git a/core/modules/datetime/tests/src/Functional/DateTestBase.php b/core/modules/datetime/tests/src/Functional/DateTestBase.php
index 369e793..d440ec9 100644
--- a/core/modules/datetime/tests/src/Functional/DateTestBase.php
+++ b/core/modules/datetime/tests/src/Functional/DateTestBase.php
@@ -181,4 +181,20 @@ protected function setSiteTimezone($timezone) {
       ->save();
   }
 
+  /**
+   * Massages test date values.
+   *
+   * If a date object is generated directly by a test, then it needs to be
+   * adjusted to behave like the computed date from the item.
+   *
+   * @param \Drupal\Core\Datetime\DrupalDateTime $date
+   *   A date object directly generated by the test.
+   */
+  protected function massageTestDate($date) {
+    if ($this->field->getSetting('datetime_type') === DateTimeItem::DATETIME_TYPE_DATE) {
+      // Set the default time for date-only items.
+      DateTimeItem::setDefaultDateTime($date);
+    }
+  }
+
 }