This code never goes in the loop because actual.getFileExtensions is a reference to a function, it's not actually calling the function. It happens to have a length property that's 0. You can click on Show Developer Tools from the Jasmine Spec Runner Window, the click on the Source tab and set a breakpoint in the code to see what branches it takes and inspect the structure and value of object. This should be actual.getFileExtensions().length instead.

Even better would be to only call actual.getFileExtensions() once and store it in a local var.

This block of code:

            var expectedFileExtensions;
            // Be sure that expectedFileExtensions is not undefined.  
            if (expected.fileExtensions === undefined) {
                expectedFileExtensions = [];
            } else {
                expectedFileExtensions = expected.fileExtensions;
            }

Can be replaced by this line of code:

            var expectedFileExtensions = expected.fileExtensions || [];

When initializing expectedFileExtensions, it's set to the first "truthy" element in the OR list. So, if expected.fileExtensions is undefined (or null), then it's set to [] (an empty array). This code is actually better because it checks for both undefined and null;