Unit Testing Entity Framework 7 with the In Memory Data Store

Entity Framework 7 includes a new InMemory store which is fantastic for unit testing. No more mocking DbContext or doing other dumb things!

Here's how

Start by creating a new class library project using the Class Library (package) template:

Next, add the appropriate Entity Framework dependencies to your project.json:

"dependencies": {
    "EntityFramework.Core": "7.0.0-beta7",
    "EntityFramework.Commands": "7.0.0-beta7",
    "EntityFramework.InMemory": "7.0.0-beta7"
},

and dependencies to the latest xUnit runner:

"xunit": "2.1.0-rc2-build3176",
"xunit.runner.dnx": "2.1.0-beta5-build169"

and finally, add a command to your project.json for the xUnit runner:

"commands": {
    "test": "xunit.runner.dnx"
}

Because we're awesome (seriously, don't do this in a real app, I'm just doing it here because it's easy) we're going to create a DbContext inside of this test project with a Foo entity:

public class MyContext : DbContext
{
    public MyContext()
    {
    }

    public MyContext(DbContextOptions options) : base(options)
    {            
    }

    public DbSet<Foo> Foos { get; set; }
}

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

Now create a test class:

public class MyTestClass
{
    private readonly MyContext _context;

    [Fact]
    public void FoosIsEmpty()
    {
        var foos = _context.Foos;

        Assert.Empty(foos);
    }
}

In order to set up entity framework for each test, we're going to make use of the fact that xUnit creates a new instance of a test class for each test run. This means we can use the constructor to get a clean MyContext for every single test.

public class MyTestClass
{
    public MyTestClass()
    {
        var db = new DbContextOptionsBuilder();
         db.UseInMemoryDatabase();
        _context = new MyContext(db.Options);
    }
    
    //Tests
}

The UseInMemoryDatabase call is the fun part. EF will enforce all constraints and validations, however it won't persist anything to a real database and instead hold everything in memory. Which means it's fast and disposable.

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You can also, if you're so inclined, set up a seed class to populate the in memory store with test data to use for each test. 👍

Update: The in memory store no longer supports constraints. (Embarrassingly, it didn't at time of this writing either, I was mistaken.) This is because constraints are solely a relational thing, and other types of stores don't enforce them. This is discussed in this Github issue, specifically this comment.

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