diff -u b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentSourceWithHighWaterTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentSourceWithHighWaterTest.php
--- b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentSourceWithHighWaterTest.php
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentSourceWithHighWaterTest.php
@@ -2,30 +2,104 @@
 
 namespace Drupal\Tests\comment\Kernel\Plugin\migrate\source\d6;
 
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
 /**
  * Tests the Drupal 6 comment source w/ high water handling.
  *
  * @covers \Drupal\comment\Plugin\migrate\source\d6\Comment
+ *
  * @group comment
  */
-class CommentSourceWithHighWaterTest extends CommentTestBase {
+class CommentSourceWithHighWaterTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['comment', 'migrate_drupal'];
 
   /**
    * {@inheritdoc}
    */
   public function providerSource() {
-    parent::providerSource();
+    $tests = [];
 
-    $this->tests[0]['expected_count'] = NULL;
-    $this->tests[0]['configuration'] = [
-      'high_water_property' => [
-        'name' => 'timestamp',
+    // The source data.
+    $tests[0]['source_data']['comments'] = [
+      [
+        'cid' => 1,
+        'pid' => 0,
+        'nid' => 2,
+        'uid' => 3,
+        'subject' => 'subject value 1',
+        'comment' => 'comment value 1',
+        'hostname' => 'hostname value 1',
+        'timestamp' => 1382255613,
+        'status' => 0,
+        'thread' => '',
+        'name' => '',
+        'mail' => '',
+        'homepage' => '',
+        'format' => 'testformat1',
+        'type' => 'story',
+      ],
+      [
+        'cid' => 2,
+        'pid' => 1,
+        'nid' => 3,
+        'uid' => 4,
+        'subject' => 'subject value 2',
+        'comment' => 'comment value 2',
+        'hostname' => 'hostname value 2',
+        'timestamp' => 1382255662,
+        'status' => 0,
+        'thread' => '',
+        'name' => '',
+        'mail' => '',
+        'homepage' => '',
+        'format' => 'testformat2',
+        'type' => 'page',
       ],
     ];
-    $this->tests[0]['high_water'] = $this->tests[0]['source_data']['comments'][0]['timestamp'];
-    array_shift($this->tests[0]['expected_data']);
 
-    return $this->tests;
+    $tests[0]['source_data']['node'] = [
+      [
+        'nid' => 2,
+        'type' => 'story',
+      ],
+      [
+        'nid' => 3,
+        'type' => 'page',
+      ],
+    ];
+
+    // The expected results.
+    $tests[0]['expected_data'] = [
+      [
+        'cid' => 2,
+        'pid' => 1,
+        'nid' => 3,
+        'uid' => 4,
+        'subject' => 'subject value 2',
+        'comment' => 'comment value 2',
+        'hostname' => 'hostname value 2',
+        'timestamp' => 1382255662,
+        'status' => 1,
+        'thread' => '',
+        'name' => '',
+        'mail' => '',
+        'homepage' => '',
+        'format' => 'testformat2',
+        'type' => 'page',
+      ],
+    ];
+
+    // The expected count.
+    $tests[0]['expected_count'] = NULL;
+
+    $tests[0]['configuration']['high_water_property']['name'] = 'timestamp';
+    $tests[0]['high_water'] = $tests[0]['source_data']['comments'][0]['timestamp'];
+    return $tests;
   }
 
 }
diff -u b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentTest.php
--- b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentTest.php
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentTest.php
@@ -2,17 +2,115 @@
 
 namespace Drupal\Tests\comment\Kernel\Plugin\migrate\source\d6;
 
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
 /**
  * Tests D6 comment source plugin.
  *
  * @covers \Drupal\comment\Plugin\migrate\source\d6\Comment
  * @group comment
  */
-class CommentTest extends CommentTestBase {
+class CommentTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['comment', 'migrate_drupal'];
 
+  /**
+   * {@inheritdoc}
+   */
   public function providerSource() {
-    parent::providerSource();
-    return $this->tests;
+    $tests = [];
+
+    // The source data.
+    $tests[0]['source_data']['comments'] = [
+      [
+        'cid' => 1,
+        'pid' => 0,
+        'nid' => 2,
+        'uid' => 3,
+        'subject' => 'subject value 1',
+        'comment' => 'comment value 1',
+        'hostname' => 'hostname value 1',
+        'timestamp' => 1382255613,
+        'status' => 0,
+        'thread' => '',
+        'name' => '',
+        'mail' => '',
+        'homepage' => '',
+        'format' => 'testformat1',
+        'type' => 'story',
+      ],
+      [
+        'cid' => 2,
+        'pid' => 1,
+        'nid' => 3,
+        'uid' => 4,
+        'subject' => 'subject value 2',
+        'comment' => 'comment value 2',
+        'hostname' => 'hostname value 2',
+        'timestamp' => 1382255662,
+        'status' => 0,
+        'thread' => '',
+        'name' => '',
+        'mail' => '',
+        'homepage' => '',
+        'format' => 'testformat2',
+        'type' => 'page',
+      ],
+    ];
+
+    $tests[0]['source_data']['node'] = [
+      [
+        'nid' => 2,
+        'type' => 'story',
+      ],
+      [
+        'nid' => 3,
+        'type' => 'page',
+      ],
+    ];
+
+    // The expected results.
+    $tests[0]['expected_data'] = [
+      [
+        'cid' => 1,
+        'pid' => 0,
+        'nid' => 2,
+        'uid' => 3,
+        'subject' => 'subject value 1',
+        'comment' => 'comment value 1',
+        'hostname' => 'hostname value 1',
+        'timestamp' => 1382255613,
+        'status' => 1,
+        'thread' => '',
+        'name' => '',
+        'mail' => '',
+        'homepage' => '',
+        'format' => 'testformat1',
+        'type' => 'story',
+      ],
+      [
+        'cid' => 2,
+        'pid' => 1,
+        'nid' => 3,
+        'uid' => 4,
+        'subject' => 'subject value 2',
+        'comment' => 'comment value 2',
+        'hostname' => 'hostname value 2',
+        'timestamp' => 1382255662,
+        'status' => 1,
+        'thread' => '',
+        'name' => '',
+        'mail' => '',
+        'homepage' => '',
+        'format' => 'testformat2',
+        'type' => 'page',
+      ],
+    ];
+
+    return $tests;
   }
 
 }
reverted:
--- b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentTestBase.php
+++ /dev/null
@@ -1,80 +0,0 @@
-<?php
-
-namespace Drupal\Tests\comment\Kernel\Plugin\migrate\source\d6;
-
-use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
-
-/**
- * Base class for comment source unit tests.
- */
-class CommentTestBase extends MigrateSqlSourceTestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public static $modules = ['comment', 'migrate_drupal'];
-
-  protected $tests = [];
-
-  /**
-   * {@inheritdoc}
-   */
-  public function providerSource() {
-    $this->tests = [];
-
-    // The source data.
-    $this->tests[0]['source_data']['comments'] = [
-      [
-        'cid' => 1,
-        'pid' => 0,
-        'nid' => 2,
-        'uid' => 3,
-        'subject' => 'subject value 1',
-        'comment' => 'comment value 1',
-        'hostname' => 'hostname value 1',
-        'timestamp' => 1382255613,
-        'status' => 0,
-        'thread' => '',
-        'name' => '',
-        'mail' => '',
-        'homepage' => '',
-        'format' => 'testformat1',
-        'type' => 'story',
-      ],
-      [
-        'cid' => 2,
-        'pid' => 1,
-        'nid' => 3,
-        'uid' => 4,
-        'subject' => 'subject value 2',
-        'comment' => 'comment value 2',
-        'hostname' => 'hostname value 2',
-        'timestamp' => 1382255662,
-        'status' => 0,
-        'thread' => '',
-        'name' => '',
-        'mail' => '',
-        'homepage' => '',
-        'format' => 'testformat2',
-        'type' => 'page',
-      ],
-    ];
-    $this->tests[0]['source_data']['node'] = [
-      [
-        'nid' => 2,
-        'type' => 'story'
-      ],
-      [
-        'nid' => 3,
-        'type' => 'page'
-      ],
-    ];
-
-    // The expected results.
-    $this->tests[0]['expected_data'] = $this->tests[0]['source_data']['comments'];
-    foreach ( $this->tests[0]['expected_data'] as $k => $row) {
-        $this->tests[0]['expected_data'][$k]['status'] = 1;
-    }
-
-  }
-}
diff -u b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariablePerCommentTypeTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariablePerCommentTypeTest.php
--- b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariablePerCommentTypeTest.php
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariablePerCommentTypeTest.php
@@ -30,7 +30,7 @@
       ],
       [
         'type' => 'story',
-      ]
+      ],
     ];
 
     $tests[0]['source_data']['variable'] = [
diff -u b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariableTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariableTest.php
--- b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariableTest.php
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariableTest.php
@@ -5,7 +5,7 @@
 use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
 
 /**
- * Tests comment variable source plugin.
+ * Tests d6_comment_variable source plugin.
  *
  * @covers \Drupal\comment\Plugin\migrate\source\d6\CommentVariable
  * @group comment
@@ -29,6 +29,7 @@
         'type' => 'page',
       ],
     ];
+
     $tests[0]['source_data']['variable'] = [
       [
         'name' => 'comment_page',
diff -u b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php
--- b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php
@@ -11,6 +11,7 @@
  * @group comment
  */
 class CommentTest extends MigrateSqlSourceTestBase {
+
   /**
    * {@inheritdoc}
    */
@@ -85,11 +86,28 @@
     ];
 
     // The expected results.
-    $tests[0]['expected_data'] = $tests[0]['source_data']['comment'];
-    $tests[0]['expected_data'][0]['comment_body'] = [
+    $tests[0]['expected_data'] = [
       [
-        'value' => 'This is a comment',
-        'format' => 'filtered_html',
+        'cid' => '1',
+        'pid' => '0',
+        'nid' => '1',
+        'uid' => '1',
+        'subject' => 'A comment',
+        'hostname' => '::1',
+        'created' => '1421727536',
+        'changed' => '1421727536',
+        'status' => '1',
+        'thread' => '01/',
+        'name' => 'admin',
+        'mail' => '',
+        'homepage' => '',
+        'language' => 'und',
+        'comment_body' => [
+          [
+            'value' => 'This is a comment',
+            'format' => 'filtered_html',
+          ],
+        ],
       ],
     ];
 
diff -u b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTypeTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTypeTest.php
--- b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTypeTest.php
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTypeTest.php
@@ -50,7 +50,7 @@
         'bundle' => 'comment_node_article',
         'data' => 'a:0:{}',
         'deleted' => '0',
-      ]
+      ],
     ];
     $tests[0]['source_data']['variable'] = [
       [
@@ -91,7 +91,7 @@
         'preview' => '0',
         'subject' => '1',
         'label' => 'Article comment',
-      ]
+      ],
     ];
     return $tests;
   }
diff -u b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
--- b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
@@ -216,7 +216,6 @@
       $high_water_field = $this->getHighWaterField();
       $conditions->condition($high_water_field, $high_water, '>');
       $this->query->orderBy($high_water_field);
-      $condition_added = TRUE;
     }
     if ($condition_added) {
       $this->query->condition($conditions);
@@ -278,6 +277,7 @@
         $high_water_field = $this->getHighWaterField();
         $conditions->condition($high_water_field, $high_water, '>');
         $this->query->orderBy($high_water_field);
+        $condition_added = TRUE;
       }
       if ($condition_added) {
         $this->query->condition($conditions);