Update to Drupal 8.2.4. For more information, see https://www.drupal.org/project/drupal/releases/8.2.4

core/tests/Drupal/Tests/Component/Diff/DiffFormatterTest.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace Drupal\Tests\Component\Diff;
+
+use Drupal\Component\Diff\Diff;
+use Drupal\Component\Diff\DiffFormatter;
+
+/**
+ * Test DiffFormatter classes.
+ *
+ * @coversDefaultClass \Drupal\Component\Diff\DiffFormatter
+ *
+ * @group Diff
+ */
+class DiffFormatterTest extends \PHPUnit_Framework_TestCase {
+
+  /**
+   * @return array
+   *   - Expected formatted diff output.
+   *   - First array of text to diff.
+   *   - Second array of text to diff.
+   */
+  public function provideTestDiff() {
+    return [
+      'empty' => ['', [], []],
+      'add' => [
+        "3a3\n> line2a\n",
+        ['line1', 'line2', 'line3'],
+        ['line1', 'line2', 'line2a', 'line3'],
+      ],
+      'delete' => [
+        "3d3\n< line2a\n",
+        ['line1', 'line2', 'line2a', 'line3'],
+        ['line1', 'line2', 'line3'],
+      ],
+      'change' => [
+        "3c3\n< line2a\n---\n> line2b\n",
+        ['line1', 'line2', 'line2a', 'line3'],
+        ['line1', 'line2', 'line2b', 'line3'],
+      ],
+    ];
+  }
+
+  /**
+   * Tests whether op classes returned by DiffEngine::diff() match expectations.
+   *
+   * @covers ::format
+   * @dataProvider provideTestDiff
+   */
+  public function testDiff($expected, $from, $to) {
+    $diff = new Diff($from, $to);
+    $formatter = new DiffFormatter();
+    $output = $formatter->format($diff);
+    $this->assertEquals($expected, $output);
+  }
+
+}