testing value of radio button

I rarely use radio buttons in DS and having an issue with the value test. My "lawgetform" test works for other fields but is not working to test the value of my 2 element radio button. I've got an "X" value assigned in the button def but when I test the value the form blows up. Can anyone provide an example? Here is my code that checks the button value, another field value and display an error accordingly:

if (lawForm.getFormValue("radiobutton_name") = "X") {
    if (lawForm.getFormValue("FIELD") > "799") {
   alert("FIELD must be < 800");
   return;
    }
  }