Question

I’m using entity framework and trying to unit test my data services which are using EF.
I’m not using repository and unit of work patterns.
I tried the following approach to mock the context and DbSet:

private static Mock<IEFModel> context;
private static Mock<IDbSet<CountryCode>> idbSet;

    [ClassInitialize]
    public static void Initialize(TestContext testContext)
    {
        context = new Mock<IEFModel>();

        idbSet = new Mock<IDbSet<CountryCode>>();

        context.Setup(c => c.CountryCodes).Returns(idbSet.Object);

    }

I get null “Object reference not set to an instance of an object” error for idbSet “Local”.
Is there any way to mock idbSet like this?
Thanks

Answer 1

I worked it out like this:
Created two classes named DbSetMock:

public class DbSetMock<T> : IDbSet<T>
    where T : class
{
    #region Fields

    /// <summary>The _container.</summary>
    private readonly IList<T> _container = new List<T>();

    #endregion

    #region Public Properties

    /// <summary>Gets the element type.</summary>
    public Type ElementType
    {
        get
        {
            return typeof(T);
        }
    }

    /// <summary>Gets the expression.</summary>
    public Expression Expression
    {
        get
        {
            return this._container.AsQueryable().Expression;
        }
    }

    /// <summary>Gets the local.</summary>
    public ObservableCollection<T> Local
    {
        get
        {
            return new ObservableCollection<T>(this._container);
        }
    }

    /// <summary>Gets the provider.</summary>
    public IQueryProvider Provider
    {
        get
        {
            return this._container.AsQueryable().Provider;
        }
    }

    #endregion

    #region Public Methods and Operators

    /// <summary>The add.</summary>
    /// <param name="entity">The entity.</param>
    /// <returns>The <see cref="T"/>.</returns>
    public T Add(T entity)
    {
        this._container.Add(entity);
        return entity;
    }

    /// <summary>The attach.</summary>
    /// <param name="entity">The entity.</param>
    /// <returns>The <see cref="T"/>.</returns>
    public T Attach(T entity)
    {
        this._container.Add(entity);
        return entity;
    }

    /// <summary>The create.</summary>
    /// <typeparam name="TDerivedEntity"></typeparam>
    /// <returns>The <see cref="TDerivedEntity"/>.</returns>
    /// <exception cref="NotImplementedException"></exception>
    public TDerivedEntity Create<TDerivedEntity>() where TDerivedEntity : class, T
    {
        throw new NotImplementedException();
    }

    /// <summary>The create.</summary>
    /// <returns>The <see cref="T"/>.</returns>
    /// <exception cref="NotImplementedException"></exception>
    public T Create()
    {
        throw new NotImplementedException();
    }

    /// <summary>The find.</summary>
    /// <param name="keyValues">The key values.</param>
    /// <returns>The <see cref="T"/>.</returns>
    /// <exception cref="NotImplementedException"></exception>
    public T Find(params object[] keyValues)
    {
        throw new NotImplementedException();
    }

    /// <summary>The get enumerator.</summary>
    /// <returns>The <see cref="IEnumerator"/>.</returns>
    public IEnumerator<T> GetEnumerator()
    {
        return this._container.GetEnumerator();
    }

    /// <summary>The remove.</summary>
    /// <param name="entity">The entity.</param>
    /// <returns>The <see cref="T"/>.</returns>
    public T Remove(T entity)
    {
        this._container.Remove(entity);
        return entity;
    }

    #endregion

    #region Explicit Interface Methods

    /// <summary>The get enumerator.</summary>
    /// <returns>The <see cref="IEnumerator"/>.</returns>
    IEnumerator IEnumerable.GetEnumerator()
    {
        return this._container.GetEnumerator();
    }

    #endregion
}

and EFModelMock:

public class EFModelMock : IEFModel
{
    #region Fields

    /// <summary>The country codes.</summary>
    private IDbSet<CountryCode> countryCodes;

    #endregion

    #region Public Properties

    /// <summary>Gets the country codes.</summary>
    public IDbSet<CountryCode> CountryCodes
    {
        get
        {
            this.CreateCountryCodes();
            return this.countryCodes;
        }
    }


    #endregion

    #region Public Methods and Operators

    /// <summary>The commit.</summary>
    /// <exception cref="NotImplementedException"></exception>
    public void Commit()
    {
        throw new NotImplementedException();
    }

    /// <summary>The set.</summary>
    /// <typeparam name="T"></typeparam>
    /// <returns>The <see cref="IDbSet"/>.</returns>
    /// <exception cref="NotImplementedException"></exception>
    public IDbSet<T> Set<T>() where T : class
    {
        throw new NotImplementedException();
    }

    #endregion

    #region Methods

    /// <summary>The create country codes.</summary>
    private void CreateCountryCodes()
    {
        if (this.countryCodes == null)
        {
            this.countryCodes = new DbSetMock<CountryCode>();
            this.countryCodes.Add(
                new CountryCode { CountryName = "Australia", DisplayLevel = 2,       TelephoneCode = "61" });

        }
    }

    #endregion
}

Then tested like this:

[TestClass]
public class CountryCodeServiceTest
{
    #region Static Fields

    /// <summary>The context.</summary>
    private static IEFModel context;

    #endregion

    #region Public Methods and Operators

    /// <summary>The initialize.</summary>
    /// <param name="testContext">The test context.</param>
    [ClassInitialize]
    public static void Initialize(TestContext testContext)
    {
        context = new EFModelMock();
    }

    /// <summary>The country code service get country codes returns correct data.</summary>
    [TestMethod]
    public void CountryCodeServiceGetCountryCodesReturnsCorrectData()
    {
        // Arrange
        var target = new CountryCodeService(context);
        var countryName = "Australia";
        var expected = context.CountryCodes.ToList();

        // Act
        var actual = target.GetCountryCodes();

        // Assert
        Assert.IsNotNull(actual);
        Assert.AreEqual(actual.FirstOrDefault(a => a.CountryName == countryName).PhoneCode, expected.FirstOrDefault(a => a.CountryName == countryName).TelephoneCode);
    }