angular-mocks.js v1.3.6 - Can't get $htttpBackend to mock my service call

(Thanks in advance if you have time to look at this, I might have to give up on using the nice unit test features in Angular if I can't resolve it :( )

I'm learning angularjs ("on the job") and am quite pleased with it so far.

I am now looking at writing unit tests for a controller we have developed using Jasmine and Karma.

I have managed to write some basic tests (that do not use $httpBackend) successfully.

I have looked at loads of examples on the net and on this site, but I just can't work out what I am doing wrong.

My controller will perform a JSON search when a button is clicked...

app.controller('PriceSearchCtrl', function ($scope, $http, $window) {
   ...
    // Do the search
    $scope.performSearch = function() {
        var response = $http({
            method: 'POST',
            url: 'performSearch.json',
            data: $scope.search,
            headers: {
                'Content-Type': 'application/json'
            }
        });
        response.success(function (data) {
            $scope.response = data;
            $scope.currentTab = 'response';
            $window.scrollTo(0,0);
        });
        response.error(function() {
            $scope.response = "REQUEST FAILED";
            $scope.currentTab = 'response';
            $window.scrollTo(0,0);
        });
    }
...
}));

This works fine when running for real, now I wanted to test it so I added this test to my currently passing spec...

...<other tests that are running fine>...

describe('Price Search', function() {
    afterEach(function() {
        httpBackend.verifyNoOutstandingExpectation();
        httpBackend.verifyNoOutstandingRequest();
    });

    it('should POST search to backend service and set the result', function() {
        var expectedResponse = {
                "success": true,
                "searchResults": { hello: 'world'}
        };

        $httpBackend.when('POST', 'performSearch.json', $scope.search, { 'Content-Type': 'application/json'}).respond(function() { return expectedResponse; });         

        $scope.performSearch();

        $httpBackend.flush();
        expect($scope.response).toEqual(expectedResponse);
    });
});

(The reason I am having to set request headers is because elsewhere we have set $httpProvider.defaults.headers.post['Content-Type'] to something else for other controllers)

When run, I get an error like this...

  Error: Unexpected request: [object Object] undefined
  No more request expected in C:/dev/web/src/test/angularjs/angular-mocks.js (line 1253)
  $httpBackend@C:/dev/web/src/test/angularjs/angular-mocks.js:1253:1
  $scope.performSearch@C:/dev/web/src/main/webapp/js/controllers.js:9:7746
  @C:/dev/web/src/test/angularjs/unit/search.test.js:130:4

I wanted to try and find out myself what is going on, so I added some "console.log" lines to the following place in "angular-mocks.js"...

(start line = 1156)

// TODO(vojta): change params to: method, url, data, headers, callback
function $httpBackend(method, url, data, callback, headers, timeout, withCredentials) {
    // BEGIN STUFF I ADDED
    console.log("DUMP-PARAMS");
    console.log(method);
    console.log(url);
    console.log(data);
    console.log(callback);
    console.log(headers);
    console.log(timeout);
    console.log(withCredentials);
    console.log("END-DUMP-PARAMS");
    // END STUFF I ADDED

Now when I run, I see that the following is logged...

LOG: Object{method: 'POST', url: 'performSearch.json', data: Object{searchType: 'PAX', effectiveDate: '22/1/2015', checkIn: '29/1/2015', checkOut: '1/2/2015', country: 'GB', currency: 'GBP', language: 'en', siteId: 1, clientId: 1, includeCancellationConditions: true, includePriceBreakdown: true, includeLog: true, roomRequirements: [...]}, headers: Object{Content-Type: 'application/json'}}
LOG: undefined
LOG: undefined
LOG: undefined
LOG: undefined
LOG: undefined
LOG: undefined
LOG: 'END-DUMP-PARAMS'

So it looks like all of the information ends up as an object in the "method" field (!!???!)

Out of pure frustration, I altered the method signature and added another block...

// TODO(vojta): change params to: method, url, data, headers, callback
// BAC: CHANGED PARAMS FROM (method, url, data, callback, headers, timeout, withCredentials) {
function $httpBackend(obj) {
    // STUFF I ADDED
    var method = obj.method;
    var url = obj.url;
    var data = obj.data;
    var callback = obj.callback;
    var headers = obj.headers;
    var timeout = obj.timeout;
    var withCredentials = obj.withCredentials;

    console.log("DUMP-PARAMS");
    console.log(method);
    console.log(url);
    console.log(data);
    console.log(callback);
    console.log(headers);
    console.log(timeout);
    console.log(withCredentials);
    console.log("END-DUMP-PARAMS");
    // END STUFF I ADDED

Now I get...

LOG: 'DUMP-PARAMS'
LOG: 'POST'
LOG: 'performSearch.json'
LOG: Object{searchType: 'PAX', effectiveDate: '22/1/2015', checkIn: '29/1/2015', checkOut: '1/2/2015', country: 'GB', currency: 'GBP', language: 'en', siteId: 1, clientId: 1, includeCancellationConditions: true, includePriceBreakdown: true, includeLog: true, roomRequirements: [Object{requestIndex: ..., occupancy: ...}]}
LOG: undefined
LOG: Object{Content-Type: 'application/json'}
LOG: undefined
LOG: undefined
LOG: 'END-DUMP-PARAMS'

TypeError: response is undefined in /.../controllers.js (line 9)

It looks to me like angular-mocks.js V1.3.6 is wrong, but this is probably just me going mad...

I can confirm that I do not have any version mismatches of angular + angualr-mock.. . Help!!