diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index dffe81d..b465caf 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -139,7 +139,13 @@
    * Test classes extending this class, and any classes in the hierarchy up to
    * this class, may specify individual lists of modules to enable by setting
    * this property. The values of all properties in all classes in the class
-   * hierarchy are merged.
+   * hierarchy are merged. So you do not need to re-declare modules that are
+   * declared in superclasses of your test class.
+   *
+   * An example:
+   * @code
+   * public static $modules = ['my_extra_module'];
+   * @endcode
    *
    * @see \Drupal\Tests\KernelTestBase::enableModules()
    * @see \Drupal\Tests\KernelTestBase::bootKernel()