Checking for a throw new Error with should.js and Mocha

Question

I've got an error thrown like so:

if (somethingBadHappened) {
    throw new Error('what were you thinking, batman?')
}

Now I want to write a test to check that this throws when expected:

should(MyClass.methodThatShouldThrow()).throws('what were you thinking, batman?')

But that actually throws the error. What am I doing wrong? Should.js docs are pretty light, since it inherits from assert.throws, but even the docs for that doesn't work in the 'should.js' way?

score 13 · Accepted Answer · edited Nov 20 '15 at 20:08

13

As you had found out, your code execute the function which throws the error & should doesn't get a chance to catch it.

To allow proper assertion, you need to wrap the function call in an anonymous function.

should(function ()  {MyClass.methodThatShouldThrow();} ).throw('what were you thinking, batman?')

edited Nov 20 '15 at 20:08

brandonscript

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answered Nov 20 '15 at 20:04

DJ.

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Hrm, ok except I'm getting `undefined is not a function` – brandonscript Nov 20 '15 at 20:07
AH, `throw` not `throws`. – brandonscript Nov 20 '15 at 20:07
1

And if you are using es2015, then it will more compact with arrow function for the anon function – DJ. Nov 20 '15 at 20:11

Checking for a throw new Error with should.js and Mocha

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