Check if an element contains a class in JavaScript?

Using plain JavaScript (not jQuery), Is there any way to check if an element contains a class?

Currently, I'm doing this:

var test = document.getElementById("test");

var testClass = test.className;



switch (testClass) {

  case "class1":

    test.innerHTML = "I have class1";

    break;

  case "class2":

    test.innerHTML = "I have class2";

    break;

  case "class3":

    test.innerHTML = "I have class3";

    break;

  case "class4":

    test.innerHTML = "I have class4";

    break;

  default:

    test.innerHTML = "";

}

<div id="test" class="class1"></div>

The issue is that if I change the HTML to this...

<div id="test" class="class1 class5"></div>

...there's no longer an exact match, so I get the default output of nothing (""). But I still want the output to be I have class1 because the <div> still contains the .class1 class.