Add test and fix warnings

Author: troosan

src/PhpWord/Writer/Word2007/Element/SDT.php

@@ -78,13 +78,13 @@ public function write()
      *
      * @see  http://www.datypic.com/sc/ooxml/t-w_CT_SdtText.html
      * @param \PhpOffice\Common\XMLWriter $xmlWriter
-     * @param \PhpOffice\PhpWord\Element\SDT $element
      */
-    private function writePlainText(XMLWriter $xmlWriter, SDTElement $element)
+    private function writePlainText(XMLWriter $xmlWriter)
     {
-        $xmlWriter->startElement("w:text");
-        $xmlWriter->endElement(); // w:{$type}
+        $xmlWriter->startElement('w:text');
+        $xmlWriter->endElement(); // w:text
     }
+
     /**
      * Write combo box.
      *

tests/PhpWord/Writer/Word2007/ElementTest.php

@@ -387,6 +387,7 @@ public function testSDTElements()
         $section->addSDT('comboBox')->setListItems(array('1' => 'Choice 1', '2' => 'Choice 2'))->setValue('select value');
         $section->addSDT('dropDownList');
         $section->addSDT('date')->setAlias('date_alias')->setTag('my_tag');
+        $section->addSDT('plainText');
 
         $doc = TestHelperDOCX::getDocument($phpWord);
 
@@ -405,6 +406,8 @@ public function testSDTElements()
         $this->assertTrue($doc->elementExists($path . '[3]/w:sdt/w:sdtPr/w:date'));
         $this->assertTrue($doc->elementExists($path . '[3]/w:sdt/w:sdtPr/w:alias'));
         $this->assertTrue($doc->elementExists($path . '[3]/w:sdt/w:sdtPr/w:tag'));
+
+        $this->assertTrue($doc->elementExists($path . '[4]/w:sdt/w:sdtPr/w:text'));
     }
 
     /**