Mocking Entity Framework Core DBContext for unit testing

In my new project, we use EF Core for ORM. We have unit tests for the repository layer where the DbContext is used. I’m going to show how to use in-memory database to create the DbContext.

I’ll use the model below for example

public class Article
{
  [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
  public int ArticleNumber { get; set; }
  public Guid Id { get; set; }
  public string Name { get; set; }
}

The DbContext looks like below

public class ArticleDbContext : DbContext
{
    public DbSet<Article> Articles { get; set; }

    // More DbSet goes here

    public ArticleDbContext(DbContextOptions<ArticleDbContext> options) : base(options)
    {}

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Model creating logic goes here
    }
}

I have a ArticleRepository as below

public interface IArticleRepository
{
    Article GetById(Guid id);
}

public class ArticleRepository : IArticleRepository
{
    private readonly ArticleDbContext _context;

    public ArticleRepository(ArticleDbContext context)
    {
        _context = context;
    }

    public Article GetById(Guid id)
    {
        return _context.FirstOrDefault(x => x.Id == id);
    }
}

 

In the test project, I have a InMemoryDbContextFactory which looks like below

public class InMemoryDbContextFactory
{
    public ArticleDbContext GetArticleDbContext()
    {
        var options = new DbContextOptionsBuilder<ArticleDbContext>()
                        .UseInMemoryDatabase(databaseName: "InMemoryArticleDatabase")
                        .Options;
        var dbContext = new ArticleDbContext(options);

        return dbContext;
    }
}

How it is used in a unit test

[TestFixture]
public class ArticleRepositoryTests
{
    private readonly ArticleDbContext _dbContext;
    private readonly IArticleRepository _articleRepository;

    public ArticleRepositoryTests()
    {
        _dbContext = new InMemoryDbContextFactory().GetArticleDbContext();
        _articleRepository = new ArticleRepository(_dbContext);
    }

    [Test]
    public GetById_Should_Return_Correct_Article()
    {
        // Arrange
        var articleId = Guid.NewGuid();
        var articles = new List<Article>
        {
            new Article { Id = Guid.NewGuid() },
            new Article { Id = Guid.NewGuid() },
            new Article { Id = articleId },
            new Article { Id = Guid.NewGuid() }
        };
        _dbContext.Articles.AddRange(articles);
        _dbContext.SaveChanges();

        // Act
        var actual = await _articleRepository.GetById(articleId);

        // Assert
        actual.Id.Should().Be(articleId);
    }
}