Issue #2891968 by Steven Jones: Tests are broken on 8.3

src/Tests/ImageEffectsTest.php

@@ -7,6 +7,6 @@ namespace Drupal\imageapi_optimize\Tests;
  *
  * @group image
  */
-class ImageEffectsTest extends \Drupal\image\Tests\ImageEffectsTest {
+class ImageEffectsTest extends \Drupal\Tests\image\Functional\ImageEffectsTest {
   public static $modules = array('imageapi_optimize',);
 }

src/Tests/ImageFieldWidgetTest.php

@@ -7,6 +7,6 @@ namespace Drupal\imageapi_optimize\Tests;
  *
  * @group image
  */
-class ImageFieldWidgetTest extends \Drupal\image\Tests\ImageFieldWidgetTest {
+class ImageFieldWidgetTest extends \Drupal\Tests\image\Functional\ImageFieldWidgetTest {
   public static $modules = array('imageapi_optimize',);
 }

src/Tests/ImageStyleDeleteTest.php

@@ -7,6 +7,6 @@ namespace Drupal\imageapi_optimize\Tests;
  *
  * @group image
  */
-class ImageStyleDeleteTest extends \Drupal\image\Tests\ImageStyleDeleteTest {
+class ImageStyleDeleteTest extends \Drupal\Tests\image\Functional\ImageStyleDeleteTest {
   public static $modules = array('imageapi_optimize',);
 }