Fail a test with Chai.js

Question

In JUnit you can fail a test by doing:

fail("Exception not thrown"); 

What's the best way to achieve the same using Chai.js?

Answer 1

There's assert.fail(). You can use it like this:

assert.fail(0, 1, 'Exception not thrown'); 

Answer 2

There are many ways to fake a failure – like the assert.fail() mentioned by @DmytroShevchenko –, but usually, it is possible to avoid these crutches and express the intent of the test in a better way, which will lead to more meaningful messages if the tests fail.

For instance, if you expect a exception to be thrown, why not say so directly:

expect( function () {     // do stuff here which you expect to throw an exception } ).to.throw( Error ); 

As you can see, when testing exceptions, you have to wrap your code in an anonymous function.

Of course, you can refine the test by checking for a more specific error type, expected error message etc. See .throw in the Chai docs for more.