Test that event handler is called when file input receives data

Is there another way to manually assign the value of the input field

You can't assign value to input[type="file"] due to security reasons.

or at least get it to send an event that is handled by fileChange

You can fire change event after spyOn:

spyOn(component, 'fileChange');
input.dispatchEvent(new Event('change'));
expect(component.fileChange).toHaveBeenCalled();

Plunker Example