diff -u b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeReviewPageTestBase.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeReviewPageTestBase.php
--- b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeReviewPageTestBase.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeReviewPageTestBase.php
@@ -82,7 +82,7 @@
     }
     $edits = $this->translatePostValues($edit);
 
-    // Enable all modules in the source
+    // Enable all modules in the source.
     $this->sourceDatabase->update('system')
       ->fields(['status' => 1])
       ->condition('type', 'module')
@@ -101,7 +101,7 @@
     $this->drupalPostForm(NULL, $edits, t('Review upgrade'));
     $this->drupalPostForm(NULL, [], t('I acknowledge I may lose data. Continue anyway.'));
 
-    // Ensure there are no errors about the missing modules from the test module.
+    // Ensure there are no errors about missing modules from the test module.
     $session = $this->assertSession();
     $session->pageTextNotContains(t('Source module not found for migration_provider_no_annotation.'));
     $session->pageTextNotContains(t('Source module not found for migration_provider_test.'));
diff -u b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTest.php
--- b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTest.php
@@ -132,7 +132,7 @@
     $this->drupalPostForm(NULL, [], t('I acknowledge I may lose data. Continue anyway.'));
     $session->statusCodeEquals(200);
     $session->pageTextContains('Upgrade analysis report');
-    // Ensure there are no errors about the missing modules from the test module.
+    // Ensure there are no errors about missing modules from the test module.
     $session->pageTextNotContains(t('Source module not found for migration_provider_no_annotation.'));
     $session->pageTextNotContains(t('Source module not found for migration_provider_test.'));
     $session->pageTextNotContains(t('Destination module not found for migration_provider_test'));
diff -u b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php
--- b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d6/MigrateUpgrade6Test.php
@@ -25,6 +25,13 @@
   /**
    * {@inheritdoc}
    */
+  protected function getSourceBasePath() {
+    return __DIR__ . '/files';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   protected function getEntityCounts() {
     return [
       'aggregator_item' => 1,