Writing a unit test for an angular controller or factory that uses Restangular shouldn't be hard, but it is. Here's how to set it up.

foo-service.js

angular.factory('foo', ['Restangular', (Restangular) => {
  return Restangular.one('foo', 1);
}]);

foo-service.spec.js

describe('foo factory', () => {
  // ...
  // test setup stuff goes here
  // ...
  let subject, value;
  beforeEach(done => {
    inject(_foo_ => {
      subject = _foo_;
    });

    // Restangular and $httpBackend require a rootScope instance because reasons
    $scope = $rootScope.$new();
    $httpBackend.expectGET('/foo/1').respond({foo: 'bar'});
    let promise = subject.get();
    
    // Flushing $httpBackend is required because reasons
    $httpBackend.flush();
    promise.then(data => {
      value = data;
      // done is a native jasmine.js function that tells the specrunner to move on to the next task.
      // Very handy for async specs.
      done();
    });
    
    // $scope.$digest() must be called to resolve the promise and trigger the callback
    $scope.$digest();
  });

  afterEach(() => {
    value = $scope = subject = null;
  });
  
  it('should return value', () => {
    expect(value.foo).toBe('bar');
  });
})