How do I mock a service that returns promise in AngularJS Jasmine unit test?

I'm not sure why the way you did it doesn't work, but I usually do it with the spyOn function. Something like this:

describe('Testing remote call returning promise', function() {  var myService;  beforeEach(module('app.myService'));  beforeEach(inject( function(_myService_, myOtherService, $q){    myService = _myService_;    spyOn(myOtherService, "makeRemoteCallReturningPromise").and.callFake(function() {        var deferred = $q.defer();        deferred.resolve('Remote call result');        return deferred.promise;    });  }  it('can do remote call', inject(function() {    myService.makeRemoteCall()      .then(function() {        console.log('Success');      });      }));

Also remember that you will need to make a $digest call for the then function to be called. See the Testing section of the $q documentation.

------EDIT------

After looking closer at what you're doing, I think I see the problem in your code. In the beforeEach, you're setting myOtherServiceMock to a whole new object. The $provide will never see this reference. You just need to update the existing reference:

beforeEach(inject( function(_myService_, $q){    myService = _myService_;    myOtherServiceMock.makeRemoteCallReturningPromise = function() {        var deferred = $q.defer();        deferred.resolve('Remote call result');        return deferred.promise;       };  }

We can also write jasmine's implementation of returning promise directly by spy.

spyOn(myOtherService, "makeRemoteCallReturningPromise").andReturn($q.when({}));

For Jasmine 2:

spyOn(myOtherService, "makeRemoteCallReturningPromise").and.returnValue($q.when({}));

(copied from comments, thanks to ccnokes)

describe('testing a method() on a service', function () {        var mock, service    function init(){         return angular.mock.inject(function ($injector,, _serviceUnderTest_) {                mock = $injector.get('service_that_is_being_mocked');;                                    service = __serviceUnderTest_;            });    }    beforeEach(module('yourApp'));    beforeEach(init());    it('that has a then', function () {       //arrange                           var spy= spyOn(mock, 'actionBeingCalled').and.callFake(function () {            return {                then: function (callback) {                    return callback({'foo' : "bar"});                }            };        });        //act                        var result = service.actionUnderTest(); // does cleverness        //assert         expect(spy).toHaveBeenCalled();      });});