Checking For Value Of Text

I have the following:

<script language="JavaScript">
<!--
window.onload=function (){
var pwinput1 = document.getElementById("tfOtherJobTitle");
pwinput1.onkeyup= function(){
if(this.value = "test"){
document.getElementById("pbRegistration").disabled=false;
}
}
}
</script>

for a button called "pbRegistration" that checks to see if the value of textbox (tfOtherJobTitle) equals "test" and on completion of the typing "test", it enables the button. Why isn't it working?