Print message on expect() assert failure

Question

Is there a way to print a custom error message when a Jasmine expect() fails?

As an example, for end to end testing I have an array of web pages and I u

Answer 1

This is what I'm using for Jasmine 2.6.4 with TypeScript (Jasmine+Chutzpah in Visual Studio).

The latest Jasmine version via NuGet seems to be 2.6.4 so I don't have the "withContext" thing (it also seems a bit of a clumsy way to do it, I prefer just to tag a message on the end of the matcher like many other frameworks).

Even though the "expectationFailOutput" parameter (the message to display) is present in the jasmine.d.ts typings it seems it it not officially supported by jasmine:

• https://github.com/jasmine/jasmine/issues/1457
• https://github.com/jasmine/jasmine/issues/1682

However, unofficially, it seems to work just fine for all except the toEqual matcher.

I use the following to add a new toBeEqualTo matcher globally which I copied from the original toEqual matcher and simply add the expectationFailOutput message to the end. The interface declaration bit lets us use expect(...).toBeEqualTo(...) without TypeScript complaining.

Example usage:

expect(x).toBe(y, "Some Message"); // stock message works with .toBe
expect(x).toEqual(y, "This is ignored"); // stock message ignored with .toEqual
expect(x).toBeEqualTo(y, "My message is displayed"); // new matcher added below

TypeScript implementation:

/// 

declare namespace jasmine
{
    interface Matchers
    {
        toBeEqualTo(expected: any, expectationFailOutput?: any): boolean;
    }
}

beforeEach(function ()
{
    jasmine.addMatchers({
        toBeEqualTo: function (util, customEqualityTesters)
        {
            customEqualityTesters = customEqualityTesters || [];

            return {
                compare: function (actual, expected, expectationFailOutput)
                {
                    var diffBuilder = (jasmine).DiffBuilder();

                    return {
                        pass: util.equals(actual, expected, customEqualityTesters, diffBuilder),

                        message: diffBuilder.getMessage() + ": " + expectationFailOutput
                    };
                }
            };
        }
    });
});