Running tests against a SQL Server is time-consuming, error-prone, and potentially costly. Establishing a connection to a database takes time, and remember, you want your test suite to be lightning-fast. It might also be a problem to rely on data if the database is used by others, whether in a development environment, by quality assurance engineers, and so on. You certainly wouldn't want to run your integration tests against a production database. Additionally, running tests against a database hosted in the cloud (for example, AWS, Azure, and so on) could potentially incur a dollar cost in terms of bandwidth and processing.

Luckily, it's quite trivial to configure a solution that uses Entity Framework to use an InMemory database.

First, install a NuGet package for the InMemory database.

Microsoft.EntityFrameworkCore.InMemory

Now, modify the test you created before so that the database context is created InMemory:

[Fact]
public void ItExists()
{
  var options = new DbContextOptionsBuilder<SpeakerMeetContext>()
      .UseInMemoryDatabase("SpeakerMeetInMemory")
      .Options;

  var context = new SpeakerMeetContext(options);

  var repository = new Repository.Repository<Speaker>(context);
}

The test should now pass because the context is now being created InMemory.

Next, create a test to verify that a collection of Speaker entities is returned when the GetAll method is called:

[Fact]
public void GivenSpeakersThenQueryableSpeakersReturned()
{
  using (var context = new SpeakerMeetContext(_options))
  {
    // Arrange
    var repository = new Repository.Repository<Speaker>(context);

    // Act
    var speakers = repository.GetAll();

    // Assert
    Assert.NotNull(speakers);
    Assert.IsAssignableFrom<IQueryable<Speaker>>(speakers);
  }
}

Now, turn your attention to the Get method in the repository. Create a new test method to verify that a null Speaker entity is returned when a speaker with the given ID is not found:

[Fact]
public void GivenSpeakerNotFoundThenSpeakerNull()
{
  using (var context = new SpeakerMeetContext(_options))
  {
    // Arrange
    var repository = new Repository.Repository<Speaker>(context);

    // Act
    var speaker = repository.Get(-1);

    // Assert
    Assert.Null(speaker);
  }
}

This should pass right away. Now, create a test to verify that a Speaker entity is returned when a speaker with the supplied ID exists:

[Fact]
public void GivenSpeakerFoundThenSpeakerReturned()
{
  using (var context = new SpeakerMeetContext(_options))
  {
    // Arrange
    var repository = new Repository.Repository<Speaker>(context);

    // Act
    var speaker = repository.Get(1);

    // Assert
    Assert.NotNull(speaker);
    Assert.IsAssignableFrom<Speaker>(speaker);
  }
}

This test will not pass quite yet. Regardless of whether or not a Speaker with the ID of 1 exists in your development database, the speakers table in the InMemory database is currently empty. Adding data to the InMemory database is quite simple.