AngularJS $http mock respond(...): how to mock a `location` header in the response?

I have an API that responds status 202 with no data, but the response has a header "Location" that points to a URL.

I've looked at the $httpBackend respond(...) documentation and see no mention of how to mock a header in the response.

I've taken a guess that it might be something like this:

var expectedUrl = 'http://...';
var responseConfig = {
    headers: {
        location: 'http://...'
    }
};
$httpBackend.when(expectedUrl).respond(202, '', responseConfig);

In my unit tests, I'm getting expected status 202, but the headers('location') is returning undefined.

Suggestions?