public async void AddingStringQuestion()
{
var questionnaire = _dbMock.Object.Questionnaires.First(q => q.Id == 1);
var expectedQuestion = _dbMock.Object.Questions.OfType <StringQuestion>().First();
var question = await _questionnaireService.AddQuestion(questionnaire.Id, expectedQuestion);
Assert.NotNull(_questionnaireService.GetQuestionFromQuestionnaire(questionnaire.Id, question.Id));
Assert.Equal(expectedQuestion.Contents, question.Contents);
_dbMock.Verify(x => x.SaveChangesAsync(), Times.Once);
}