diff -u b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php
--- b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php
+++ b/core/modules/migrate/tests/src/Kernel/MigrateSourceTestBase.php
@@ -34,8 +34,17 @@
   /**
    * The data provider.
    *
-   * @see testSource for the elements that should be included in each data set
-   * returned by this method.
+   * Each data set should consist of the following elements:
+   *
+   *  - An array of source data, which can be optionally processed and set up
+   *    by subclasses.
+   *  - An array of expected result rows.
+   *  - (optional) The number of result rows the plugin under test is expected
+   *    to return. If this is not a numeric value, the plugin will not be
+   *    counted.
+   *  - (optional) Array of configuration options for the plugin under test.
+   *
+   * @see testSource
    *
    * @return array
    */
diff -u b/core/modules/user/tests/src/Kernel/Plugin/migrate/source/d7/RoleTest.php b/core/modules/user/tests/src/Kernel/Plugin/migrate/source/d7/RoleTest.php
--- b/core/modules/user/tests/src/Kernel/Plugin/migrate/source/d7/RoleTest.php
+++ b/core/modules/user/tests/src/Kernel/Plugin/migrate/source/d7/RoleTest.php
@@ -10,7 +10,7 @@
  * @covers \Drupal\user\Plugin\migrate\source\d7\Role
  * @group user
  */
-class RoleTest extends MigrateSqlSourceTestBase  {
+class RoleTest extends MigrateSqlSourceTestBase {
 
   /**
    * {@inheritdoc}