使用存根和模拟进行单元测试

Question

I'm trying to write tests for some classes. The classes I want to test use different repositories to to get and save things from my database.

A simplified example

public class MyClass
{
    private readonly IGroupRepository _groupRepo;

  public MyClass(IGroupRepository groupRepo){ 
    _groupRepo = groupRepo; 
  }

  public void Execute(PersonInfo personInfo, string id){
  var group = _groupRepo.GetById(id);

  var person = group.Persons.First(p=> p.Id == personInfo.Id);

  person.FirstName = personInfo.FirstName;
  person.LastName = personInfo.LastName;

  _groupRepo.Save(group);      
  }
}

What I want to do is make sure that what is saved into the db is correct.

So I have a unit test like this:

[TestMethod]
public void TestMethod(){
    var groupId = "ABC";
    var personId = 1;

    ver personInfo = new PersonInfo()
    {
      Id = personId,
      FirstName = "Sam",
      LastName = "Smith"  
    }

    var groupStub = new Mock<IGroupRepository>;
    groupStub.Setup(x=> x.GetById(groupId)).Returns(new Group(){
            Id = groupId,
            Persons = List<Person>()
            {
                new Person()
                {
                    Id = personId,
                    FirstName = "George",
                    LastName = "Bolton",
                }
            }
        }
    });

    var myClass = new MyClass();
    myClass.Execute(personInfo, groupId);

    var group = groupStub.GetById(groupId);
    var person = group.Persons.First(p=> p.Id == personId);

    Assert.AreEqual(personInfo.FirstName, person.FirstName);
}

I thought this was fine, but then I was reading more up on it and I read that you are not supposed to assert on a sub, which I think I'm doing in my assert statement? I'm getting info from the stub, then using Assert on the result?

So I'm not sure if this is the correct way to test. If not, why and what is the correct way?

Answer 1

It is not recommended that you should be testing what is saved into the database is correct. It is more of integration testing than unit testing, and it goes beyond the scope of you class.

There could be many reasons for data not getting saved properly in db, but your class is behaving as it should be, for example network issue, but then failing your UT will not be correct.

Instead you should test your class for scenarios where how your class behaves when database insertions fails, or if some exception occurs. And then use your mocking framework to mock repository with those expectations and assert accordingly in tests of your class.

Some good readings here and here

Answer 2

You should not test the logic of another module/class that is being used in the class you are implementing Unit test.

You should only test/verify that the call to that module is being invoked or not as your business logic says. You should only concentrate on the Business logic of that class only for what you are writing unit testcases.

Here in your case IGroupRepository is another module/class and not the one for which you are writing unit tests. Instead if you want to verify that data is being saved or not then you should include that in another test case which you are implementing for IGroupRepository.

However writing unit tests for data saving is not recommended and it is considered as part of integration test.

Answer 3

Yes, you are correct that there is something wrong with how the test is written. In fact, you are not testing MyClass . You are instead testing that the mocking framework you use works. As proof, comment the two lines that use MyClass and run the test again. It will still pass:

[TestMethod]
public void TestMethod()
{
    var groupId = "ABC";
    var personId = 1;

    ver personInfo = new PersonInfo()
    {
      Id = personId,
      FirstName = "Sam",
      LastName = "Smith"  `
    }

    var groupStub = new Mock<IGroupRepository>;
    groupStub.Setup(x=> x.GetById(groupId)).Returns(new Group(){
            Id = groupId,
            Persons = List<Person>()
            {
                new Person()
                {
                    Id = personId,
                    FirstName = "George",
                    LastName = "Bolton",
                }
            }
        }
    });

    // var myClass = new MyClass();
    // myClass.Execute(personInfo, groupId);

    var group = groupStub.GetById(groupId);
    var person = group.Persons.First(p=> p.Id == personId);

    Assert.AreEqual(personInfo.FirstName, person.FirstName);
}

What generally helps me in writing unit tests, is asking myself first what behaviour I am really testing. In this particular case, I believe you want to test that when calling MyClass.Execute , you expect that IGroupRepository.Save is called with the person's name changed.

Writing that assertion in the mocking framework I am familiar with (NSubstitute), looks like this:

groupStub.Received().Save(
    Arg.Is<Group>(group =>
    {
        return groupId.Id == groupId && 
            group.Persons[0].Id == personId &&
            group.Persons[0].FirstName == "Sam" &&
            group.Persons[0].LastName == "Smith";
    });

There should be something similar in the mocking framework you use.