Script error (:0) when trying to run async test in mocha-phantomjs

Question

i'm trying to test a piece of asynchronous code but sadly enough i'm getting an obscure error code and i cant seem to figure out what the issue is. The test runs fine in the browser but running it in phantomjs results in:

Uncaught Script error. (:0)

The test is written as an requirejs module and has a dependency on another module. Like i said this works fine in the browser, and when doing none async tests everything works fine in phantomjs as well. I'm using phantomjs 1.9.12 and mocha-phantomjs 3.4.1.

define([ "csl" ], function( csl ) 
{  
   describe( "CSL", function()
   {
      it( "isLoggedIn", function( testCompleted )
      {
          csl.isLoggedIn().then( function( partner )
          {
              chai.expect( partner ).to.be.a( "object" );
              testCompleted();
          } )
          .fail( function( error )
          {
               testCompleted( error );
          } );
      } );
  } );
} );

Answer 1

That is the error that mocha produces when there is an exception in an async function, and chai.expect can throw an AssertionError.

You can reproduce the same error in a browser with a simple timeout:

    it("should fail async", function(done) {
        window.setTimeout(function() {
            "".should.not.equal("");
            done();
        })
    })

To fix it, you need to report the error via the callback rather than exceptions:

    it("should fail async with good error", function(done) {
        window.setTimeout(function() {
            if ("" == "") return done(new Error("Async error message"));
            done();
        })
    })

    it("should fail async with exception", function(done) {
        window.setTimeout(function() {
            try {
                "".should.not.equal("");
            }
            catch (e) {
                return done(e);
            }
            done();
        })
    })

The problem isn't with phantom itself (other than whatever is making the test fail) but the connection between the test runner and phantom makes everything asynchronous, triggering the mocha bug.