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throw

  • to[.not].throw

The throw assertion ensures that a function throws an exception.

For example:

function foo () {
    throw new Error('Something bad happened');
}

expect(foo).to.throw();

The error message can also be checked:

expect(foo).to.throw('Something bad happened');

When checking the message as above, the test defaults to a substring search. This deals with error prefixing like "Error: Something bad happened" as well as suffixing like "Something bad happened at line 3 of somefile".

To do a full message equality test, add the exactly modifier:

expect(foo).to.exactly.throw('Something bad happened');