Recreate and Reseed LocalDb Before Each Unit Test

Question

I'm attempting to write unit/integration tests for my ASP.NET Web API project and struggling to run each test in isolation. Allow me to explain.

I have a *.testsettings file with deployment settings configured. Before each test run, an empty *.mdf file is deployed to the test location. Since I'm using Entity Framework Code First, I can use a database initializer to push my schema to the database and seed a particular table with 2 rows. This works great.

The problem I'm facing is that the various tests for all of my ApiControllers' actions can step on each other's toes if they execute in the wrong order. For example, if I run the GET test before the POST test then GET returns 2 objects with if they are run in the reverse order then GET returns 3 objects.

What I think I need to do is drop, recreate and reseed my database before every test. Is this a good idea or is there are better way? If this is the best I can do, I would I go about resetting my database before each test.

Answer 1

Here's what I ended up doing for anyone that is interested.

I extended DropCreateDatabaseAlways<TContext> and overrode the Seed method to populate my database with known test data that my unit tests can rely on.

public class MyDatabaseInitializer : System.Data.Entity.DropCreateDatabaseAlways<MyDbContext>
{
    protected override void Seed(MyDbContext context)
    {
        // Add entities to database.

        context.SaveChanges();
    }
}

I then implemented an [AssemblyInitialize] method which sets the database initializer.

[TestClass]
public class Global
{
    [AssemblyInitialize]
    public static void AssemblyInitialize(TestContext context)
    {
        System.Data.Entity.Database.SetInitializer(new MyDatabaseInitializer());
    }
}

This sets the initializer for the database but does not actually run it. The intitializer is run in a [TestInitialize] method I wrote which forces the database to be dropped, recreated and reseeded before each test.

[TestClass]
public class MyTestClass
{
    [TestInitialize]
    public void TestInitialize()
    {
        MyDbContext context = new MyDbContext();
        context.Database.Initialize(true);
    }

    [TestMethod]
    public void MyUnitTest()
    {
        Assert.IsTrue(true);
    }
}

Answer 2

I would suggest re-creating your database before you begin your tests and then wrap each in a transaction that always rolls back. This is quite beneficial if your recreate stage takes a lot of time to complete (e.g. because of the actions that need to be performed, etc.).

Answer 3

In our current setup we're recreating the database schema before each class is loaded (with ClassInitialize attribute, but this could definitely be moved to AssemblyInitialize), and just seeding/cleaning up the database with the appropriate records before/after each test run (with TestInitialize/TestCleanup attribute).

More info: http://msdn.microsoft.com/en-us/library/ms379625(v=vs.80).aspx