tests: Use ::class for DOMDocument class name

Also capitalize it properly.

(cherry picked from commit 90869d8)

Author: jtojnar

tests/ReadabilityTest.php

@@ -19,15 +19,15 @@ public function testConstructDefault()
         $readability = $this->getReadability('');
 
         $this->assertNull($readability->url);
-        $this->assertInstanceOf('DomDocument', $readability->dom);
+        $this->assertInstanceOf(\DOMDocument::class, $readability->dom);
     }
 
     public function testConstructHtml5Parser()
     {
         $readability = $this->getReadability('<html/>', 'http://0.0.0.0', 'html5lib');
 
         $this->assertSame('http://0.0.0.0', $readability->url);
-        $this->assertInstanceOf('DomDocument', $readability->dom);
+        $this->assertInstanceOf(\DOMDocument::class, $readability->dom);
         $this->assertSame('<html/>', $readability->original_html);
     }
 
@@ -39,7 +39,7 @@ public function testConstructSimple()
         $readability = $this->getReadability('<html/>', 'http://0.0.0.0');
 
         $this->assertSame('http://0.0.0.0', $readability->url);
-        $this->assertInstanceOf('DomDocument', $readability->dom);
+        $this->assertInstanceOf(\DOMDocument::class, $readability->dom);
         $this->assertSame('<html/>', $readability->original_html);
         $this->assertTrue($readability->tidied);
     }
@@ -52,15 +52,15 @@ public function testConstructDefaultWithoutTidy()
         $this->assertSame('', $readability->original_html);
         $this->assertFalse($readability->tidied);
 
-        $this->assertInstanceOf('DomDocument', $readability->dom);
+        $this->assertInstanceOf(\DOMDocument::class, $readability->dom);
     }
 
     public function testConstructSimpleWithoutTidy()
     {
         $readability = $this->getReadability('<html/>', 'http://0.0.0.0', 'libxml', false);
 
         $this->assertSame('http://0.0.0.0', $readability->url);
-        $this->assertInstanceOf('DomDocument', $readability->dom);
+        $this->assertInstanceOf(\DOMDocument::class, $readability->dom);
         $this->assertSame('<html/>', $readability->original_html);
         $this->assertFalse($readability->tidied);
     }