Jasmine expect toThrow not passing nor catching

Question

Trying to use expect(fn).toThrow() in protractor.

The function (fn) I'm passing returns a promise (protractor.promise.defer) which protractor supposedly forces expect() to deal with properly.

Upon running, instead of catching the error and/or passing the test, it does neither.

• "Expected function to throw an error"
• "Wait timed out after ~3000ms"
  • (Thrown by browser.wait()'s timeout parameter)

I have tried using:

• deferred.reject() which throws a catchable error
  • Normally caught by using .thenCatch() instead of .then() on a promising function
• deferred.fulfill() and throwing an error in the function "manually"
  • Using syntax throw new Error();
  • and throw {name: 'Error', message: 'timed out'}
  • and throw {name: 'Exception'}
• I have tried removing .fulfill() and .reject(), meaning the only way for the expect to move on is for the error to get thrown.
• I have even removed all return statements, so that the expect won't finish the function unless it throws the error.
• Update: tried using .toThrowError() instead of .toThrow()
• Update: tried override .toThrow() via custom matchers, but I have no idea how to make the anonymous function in .thenCatch() make the original matcher return its result object without returning a promise.

Everytime the expect fails and the error is still thrown and uncaught (exactly as the syntax says it will be thrown).

My hunches are:

• Is protractor not overriding expect properly for this case?
• Is it because the throw happens in an anonymous function passed to a .then(function(){ /*error thrown here*/ }) and not the original fn function?
• Can I make a jasmine custom matcher return a promise to return the result later? (Does protractor account for those promises too?) Then I would just override the original .toThrow() method to account for the possibility.
• Or am I just overlooking something that simple?

Answer 1

Chai as Promised might help to have a cleaner syntax, e.g. something like:

expect(fn_returning_promise()).to.eventually.be.rejectedWith(...)

Answer 2

Assuming your promise will be fulfilled/rejected later in time (async), you can't rely on the expect(function() {..}.toThrow() to work in that case.

What I would do is something like this (not used to protractor promises):

it('.....', function(done) {
    MyPromise(...)
        .then(... my normal process which should throw....)
        .then(function() { 
                   // Error not thrown by the process, so fail the test.
                   expect(true).toBe(false);
              },
              function(err) {
                   // Expected error thrown so pass the test.
                   done();
              });
});

Assuming this is how you catch errors with protractor promises ?

Some other implementation have a .catch() method you can chain.