How can I test for equality to a bound function when unit testing?

Instead of

expect(bar.register.calls.argsFor(0)[0]).toEqual(bar.handler);

you can do

expect(Object.create(bar.handler.prototype) instanceof bar.register.calls.argsFor(0)[0])
  .toBe(true);

expect(Object.create(bar.handler.prototype)).
  toEqual(jasmine.any(bar.register.calls.argsFor(0)[0]));

This works because the internal [[HasInstance]] method of the bound function delegates to the [[HasInstance]] method of the original function.

This blog post has a more detailed analysis of bound functions.

this.handler.bind(this) creates completely a new function, therefore it is not equal to bar.handler. See Function.prototype.bind().

You can pass bounded function as argument to your initialize function and then test it, e.g.:

var handler = bar.handler.bind(bar);
bar.initialize(handler);
expect(bar.register.calls.argsFor(0)[0]).toEqual(handler);

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