Asserting that a function throws exceptions with Qunit

Question

I am new to Qunit and unit testing. I am trying to figure out what and how to test the following function. It does not do much at the moment but I wanted to assert that if I pass it incorrect values that errors are being thrown: ``` function attrToggle (panel, attr) { 'use strict'; if (!panel) { throw new Error('Panel is not defined'); } if (!attr) { throw new Error('Attr is not defined'); } if (typeof panel !== 'string') { throw new Error('Panel is not a string'); } if (typeof attr !== 'string') { throw new Error('Attr is not a string'); } if (arguments.length !== 2) { throw new Error('There should be only two arguments passed to this function')} }; ``` How do I go about asserting that an error will be thrown if any of these conditions are not met? I tried to look at Qunit's 'raises' assertion but think I am misunderstanding it. My interpretation would be that the test passes if an error is thrown. So if I tested something like this: ``` test("a test", function () { raises(function (…

Accepted Answer

A couple of things wrong, a working example is at http://jsfiddle.net/Z8QxA/1/

The main issue is that you are passing the wrong thing as the second argument to `raises()`. The second argument is used to verify that the correct Error has been thrown, so it either expects a regex, a constructor of the type of error, or a callback that allows you do your own verification.

So in your example, you were passing `attrToggle` as the type of error that would be thrown. Your code actually throws an `Error` type and so the check actually failed. Passing `Error` as the second argument works as you want:

```
test("a test", function () {
    raises(function () {
        attrToggle([], []);
    }, Error, "Must throw error to pass.");
});
```

Secondly, you don't need the `throw` keyword when calling `attrToggle()` inside `raises()`.

Asserting that a function throws exceptions with Qunit

Solution

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