We Test Database Operations - Introduction to Integration Testing in .NET

From my previous articles, you already know that automatic tests can be divided into, among others, unit tests and integration tests. I have already introduced you to unit tests in recent articles (if you haven't read them yet, be sure to do so). Now it's time for integration tests. In unit testing, we test single units, without external dependencies. It may turn out that we have a lot of unit tests that are green, but in fact there may be bugs in our application. We may have errors in, for example, the external dependencies mentioned earlier. To check this, we also need to write integration tests that test several units connected to each other and cooperation with external dependencies.

Why separate unit tests from integration tests?

Preparation for integration tests

What does a sample integration test written in C# look like?

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class UserRepository
{
    public void Add(User user)
    {
        using (var context = new ApplicationDbContext())
        {
            context.Users.Add(user);
            context.SaveChanges();
        }
    }
}

As you can see, this class has external dependencies - it works with the database.

#1 Database for integration tests.
To conduct tests in such a case, it is best to prepare a database for integration tests.

#2 New design for integration tests.
To avoid mixing integration tests with other tests. It is best to create a separate project with only integration tests. Thanks to this division, unit tests and integration tests can be run separately. You can name the new project Project.IntegrationTests.

#3 We install the required frameworks.
In my case it will be EntityFramework, NUnit and NUnit3TestAdapter.

#4 Configuration.
In the app.config file I complete the connection string for my test database.

#5 Test isolation.
I want the data I added to disappear from the database after each test. To do this, all my commands must be executed in a transaction. We can do this by adding our own attribute, which will then be added to each test after which we want to clean the data. We add a class, for example, called Isolated. By marking our testing class with the [Isolated] attribute, a new transaction will be created before each test, and a rollback of this transaction will be triggered after each test.

public class Isolated : Attribute, ITestAction
{
    private TransactionScope _transactionScope;

    public ActionTargets Targets
    {
        get { return ActionTargets.Test; }
    }

    public void AfterTest(ITest test)
    {
        _transactionScope.Dispose();
    }

    public void BeforeTest(ITest test)
    {
        _transactionScope = new TransactionScope();
    }
}

#6 New class for integration tests of the UserRepository class.
Sticking to convention, we add a new class to the test project called UserRepositoryTests. Here will be all the methods testing the UserRepository class.

#7 We are writing an integration test.

public class UserRepositoryTests
{
    [Test, Isolated]
    public void Add_PassValidUser_ShouldAddUserToDatabase()
    {
        var context = new ApplicationDbContext();
        var user = new User { Id = 1, Name = "name" };
        var userRepository = new UserRepository();

        userRepository.Add(user);

        var usersCount = context.Users.Count(x => x.Id == user.Id && x.Name == user.Name);
        Assert.That(usersCount, Is.EqualTo(1));
    }
}

We must remember to mark the method with the Test and Isolated attributes. We have added a method that, after passing the user, should add it to the database. First, there is the initialization of the objects that we use in the test. We add a user via the Add method of the UserRepository class. Finally, we check whether there is only one user with such data in the database. The test passes, additionally, if we run the test many times, it will always pass because after each test, a transaction rollback is performed on the database.

Unit Testing School

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