Testing a promise on Angularjs

I'm trying to apply unit testing on the following function:

 function do_query(method, url, data, callback){
        var defer = $q.defer();
        var header_request = StorageService[storage].get('header_request');
        var settings =  {
            "method": "POST",
            "url": null,
            "data": null,
            "headers": {
                "Content-Type": "application/json;charset=utf-8",
                "Authorization": header_request || StorageService.session.get("header_request") || "Basic #hash"
            }
        };

        try {
            settings.method = method.toUpperCase();
            settings.url = url;

            if(method.toUpperCase() == 'GET' && data !== undefined){
                settings.url += json2queryString(data, true);
            } else {
                settings.data = data;
            }

        } catch (e) {
            log("error", "[SettingsManageException] Could not manage settings object to entity in data: " + data);
            throw e;
        }

        if( ! StorageService[storage].get('userLogged') ){
            return defer.reject("Session expired.");
        }

        if(callback !== undefined || callback !== null){
            if(typeof callback == 'function') {
                $http(settings).then(function (res) {
                    return callback(res);
                });
            } else if(Array.isArray(callback) && callback.length == 2 &&
                typeof callback[0] == 'function' && typeof callback[1] == 'function'){
                $http(settings).then(
                    function(res){
                        return callback[0](res);
                    },
                    function(err){
                        return callback[1](err);
                    }
                );
            } else {
                return $http(settings);
            }
        } else {
            return $http(settings);
        }
    }

I can not access any of the promises. My unit tests are being done as follows:

 it('do_query to instance get for callback undefined', function(){ //
    var res = {"data": [{ "ID": 1, "NAME": "Instancia Teste", "Entity": { "Name": "instance", "Version": 2}}]};
    successSpy = jasmine.createSpy('success');
    failureSpy = jasmine.createSpy('failure');

    srv.do_query('GET', 'http://52.61.47.71:8094/stcpcore/instances', null, null).then(successSpy, failureSpy);

    httpBackend.expect('GET', 'http://52.61.47.71:8094/stcpcore/instances').respond(200, res);
    httpBackend.flush();

    expect(successSpy).toHaveBeenCalledWith(res);
    expect(failureSpy).not.toHaveBeenCalled();
}); 

it('testing do_query for condition else if', function(){         
    var callback = [srv.checkUserStatus, srv.checkUserStatus];

    srv.do_query('GET', null, null, callback); 
    expect(srv.do_query).toBeDefined(); 
}); 

How should the test be done to access this promise?