我总是收到此错误

normal.js:19 Uncaught TypeError: Cannot set property 'innerHTML' of null

这里是 html 代码：

<div id="myModal" class="modal">
    <div class="modal-content">
        <div class="modal-header">
            <span class="close">&times;</span>
            <form >
            <input class="button btn-red" type="button" name="btn" value="random" onclick="myFunction()">
            </form>
        </div>
        <div class="modal-body">
            <a id "test">...</a>
            <p>Some other text...</p>
        </div>
        <div class="modal-footer">
            <h3>Modal Footer</h3>
        </div>
    </div>

</div>

这里是 javascript 代码：

function myFunction() {
document.getElementById("test").innerHTML="Its working";}