EF6 Mocking derived DbSets

Question

I am trying to apply the new mocking of EF6 to my existing code.

I have a class that Extends DbSet. One of the methods call the base class (BdSet) Create method. Here is the a sample code (not the complete solution or real names):

public class DerivedDbSet<TEntity> : DbSet<TEntity>, IKeyValueDbSet<TEntity>, IOrderedQueryable<TEntity> where TEntity : class
{
    public virtual bool Add(string value1, string value2) {
        var entity = Create(); // There is no direct implementation of the Create method it is calling the base method
        // Do something with the values
        this.Add(entity);
        return true;
    }
}

I am mocking using the Test Doubles sample (here is the peace of code):

var data = new List<DummyEntity> {
    new DummyEntity { Value1 = "First", Value2 = "001" },
    new DummyEntity { Value1 = "Second", Value2 = "002" }
}.AsQueryable();
var mock = new Mock<DerivedDbSet<DummyEntity>>();
mock.CallBase = true;
mock.As<IQueryable<T>>().Setup(m => m.Provider).Returns(source.Provider);
mock.As<IQueryable<T>>().Setup(m => m.Expression).Returns(source.Expression);
mock.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(source.ElementType);
mock.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(source.GetEnumerator());

I've set the CallBase property to true to try to force the call to the base class...

But I keep receiving the following error:

System.NotImplementedException: The member 'Create' has not been implemented on type 'DerivedDbSet1Proxy' which inherits from 'DbSet1'. Test doubles for 'DbSet`1' must provide implementations of methods and properties that are used.

I want the call of create to fallback to the default implementation in DbSet.

Can someone help me with that?

Answer 1

After some struggle with the internal functions and async references of mocking a DbSet I came out with a helper class that solved most of my problems and might serve as base to someone implementation. Here is the code:

public static class MockHelper
{
    internal class TestDbAsyncQueryProvider<TEntity> : IDbAsyncQueryProvider {

        private readonly IQueryProvider _inner;

        internal TestDbAsyncQueryProvider(IQueryProvider inner) { _inner = inner; }
        public IQueryable CreateQuery(Expression expression) { return new TestDbAsyncEnumerable<TEntity>(expression); }
        public IQueryable<TElement> CreateQuery<TElement>(Expression expression) { return new TestDbAsyncEnumerable<TElement>(expression); }
        public object Execute(Expression expression) { return _inner.Execute(expression); }
        public TResult Execute<TResult>(Expression expression) { return _inner.Execute<TResult>(expression); }
        public Task<object> ExecuteAsync(Expression expression, CancellationToken cancellationToken) { return Task.FromResult(Execute(expression)); }
        public Task<TResult> ExecuteAsync<TResult>(Expression expression, CancellationToken cancellationToken) { return Task.FromResult(Execute<TResult>(expression)); }
    }

    internal class TestDbAsyncEnumerable<T> : EnumerableQuery<T>, IDbAsyncEnumerable<T> {
        public TestDbAsyncEnumerable(IEnumerable<T> enumerable) : base(enumerable) { }
        public TestDbAsyncEnumerable(Expression expression) : base(expression) { }
        public IDbAsyncEnumerator<T> GetAsyncEnumerator() { return new TestDbAsyncEnumerator<T>(this.AsEnumerable().GetEnumerator()); }
        IDbAsyncEnumerator IDbAsyncEnumerable.GetAsyncEnumerator() { return GetAsyncEnumerator(); }
        public IQueryProvider Provider { get { return new TestDbAsyncQueryProvider<T>(this); } }
    } 

    internal class TestDbAsyncEnumerator<T> : IDbAsyncEnumerator<T> {

        private readonly IEnumerator<T> _inner;

        public TestDbAsyncEnumerator(IEnumerator<T> inner) { _inner = inner; }
        public void Dispose() { _inner.Dispose(); }
        public Task<bool> MoveNextAsync(CancellationToken cancellationToken) { return Task.FromResult(_inner.MoveNext()); }
        public T Current { get { return _inner.Current; } }
        object IDbAsyncEnumerator.Current { get { return Current; } }
    } 

    public static Mock<TDbSet> CreateDbSet<TDbSet, TEntity>(IList<TEntity> data, Func<object[], TEntity> find = null)
        where TDbSet : class, IDbSet<TEntity>
        where TEntity : class, new() {
        var source = data.AsQueryable();
        var mock = new Mock<TDbSet> { CallBase = true };
        mock.As<IQueryable<TEntity>>().Setup(m => m.Expression).Returns(source.Expression);
        mock.As<IQueryable<TEntity>>().Setup(m => m.ElementType).Returns(source.ElementType);
        mock.As<IQueryable<TEntity>>().Setup(m => m.GetEnumerator()).Returns(source.GetEnumerator());
        mock.As<IQueryable<TEntity>>().Setup(m => m.Provider).Returns(new TestDbAsyncQueryProvider<TEntity>(source.Provider));
        mock.As<IDbAsyncEnumerable<TEntity>>().Setup(m => m.GetAsyncEnumerator()).Returns(new TestDbAsyncEnumerator<TEntity>(data.GetEnumerator()));
        mock.As<IDbSet<TEntity>>().Setup(m => m.Create()).Returns(new TEntity());
        mock.As<IDbSet<TEntity>>().Setup(m => m.Add(It.IsAny<TEntity>())).Returns<TEntity>(i => { data.Add(i); return i; });
        mock.As<IDbSet<TEntity>>().Setup(m => m.Remove(It.IsAny<TEntity>())).Returns<TEntity>(i => { data.Remove(i); return i; });
        if (find != null) mock.As<IDbSet<TEntity>>().Setup(m => m.Find(It.IsAny<object[]>())).Returns(find);
        return mock;
    }

    public static Mock<DbSet<TEntity>> CreateDbSet<TEntity>(IList<TEntity> data, Func<object[], TEntity> find = null)
        where TEntity : class, new() {
        return CreateDbSet<DbSet<TEntity>, TEntity>(data, find);
    }
}

And here is a use sample (based on the names I've given before):

var data = new List<DummyEntity> {
    new DummyEntity { Value1 = "First", Value2 = "001" } },
    new DummyEntity { Value1 = "Second", Value2 = "002" } }
};
var mockDummyEntities = MockHelper.CreateDbSet<DerivedDbSet<DummyEntities>, DummyEntities>(data, i => data.FirstOrDefault(k => k.Value2 == (string)i[0]));
var mockContext = new Mock<DummyDbContext>();
mockContext.Setup(c => c.DummyEntities).Returns(mockDummyEntities.Object);

Any suggestions on how to improve this solution is very welcome.

Regards

Answer 2

This is a modified version based on Andre that worked for me. Note, that I did not need the async references. Code will add all derived classes (if any)

Usage:

/// <summary>
/// 
/// </summary>
[TestMethod]
public void SomeTest()
{
    //Setup
    var mockContext = new Mock<FakeDbContext>();
    //SomeClass can be abstract or concrete
    mockContext.createFakeDBSet<SomeClass>();
    var db = mockContext.Object;

    //Setup create(s) if needed on concrete classes
    //Mock.Get(db.Set<SomeOtherClass>()).Setup(x => x.Create()).Returns(new SomeOtherClass());

    //DO Stuff

    var list1 = db.Set<SomeClass>().ToList();
    //SomeOtherClass derived from SomeClass
    var subList1 = db.Set<SomeOtherClass>().ToList();
    CollectionAssert.AreEquivalent(list1.OfType<SomeOtherClass>.ToList(), subList1);
}

Code:

/// <summary>
/// http://stackoverflow.com/questions/21943328/ef6-mocking-derived-dbsets
/// </summary>
public static class MoqSetupExtensions
{
    static IEnumerable<Type> domainTypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(x => x.GetTypes());
    public static Mock<DbSet<T>> createFakeDBSet<T>(this Mock<FakeDbContext> db, List<T> list = null, Func<List<T>, object[], T> find = null, bool createDerivedSets = true) where T : class
    {
        list = list ?? new List<T>();
        var data = list.AsQueryable();
        //var mockSet = MockHelper.CreateDbSet(list, find);
        var mockSet = new Mock<DbSet<T>>() { CallBase = true };
        mockSet.As<IQueryable<T>>().Setup(m => m.Provider).Returns(() => { return data.Provider; });
        mockSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(() => { return data.Expression; });
        mockSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(() => { return data.ElementType; });
        mockSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(() => { return list.GetEnumerator(); });

        mockSet.Setup(m => m.Add(It.IsAny<T>())).Returns<T>(i => { list.Add(i); return i; });
        mockSet.Setup(m => m.AddRange(It.IsAny<IEnumerable<T>>())).Returns<IEnumerable<T>>((i) => { list.AddRange(i); return i; });
        mockSet.Setup(m => m.Remove(It.IsAny<T>())).Returns<T>(i => { list.Remove(i); return i; });
        if (find != null) mockSet.As<IDbSet<T>>().Setup(m => m.Find(It.IsAny<object[]>())).Returns<object[]>((i) => { return find(list, i); });
        //mockSet.Setup(m => m.Create()).Returns(new T());

        db.Setup(x => x.Set<T>()).Returns(mockSet.Object);

        //Setup all derived classes            
        if (createDerivedSets)
        {
            var type = typeof(T);
            var concreteTypes = domainTypes.Where(x => type.IsAssignableFrom(x) && type != x).ToList();
            var method = typeof(MoqSetupExtensions).GetMethod("createFakeDBSetSubType");
            foreach (var item in concreteTypes)
            {
                var invokeResult = method.MakeGenericMethod(type, item)
                    .Invoke(null, new object[] { db, mockSet });
            }
        }
        return mockSet;
    }
    public static Mock<DbSet<SubType>> createFakeDBSetSubType<BaseType, SubType>(this Mock<FakeDbContext> db, Mock<DbSet<BaseType>> baseSet)
        where BaseType : class
        where SubType : class, BaseType
    {
        var dbSet = db.Object.Set<BaseType>();

        var mockSet = new Mock<DbSet<SubType>>() { CallBase = true };
        mockSet.As<IQueryable<SubType>>().Setup(m => m.Provider).Returns(() => { return dbSet.OfType<SubType>().Provider; });
        mockSet.As<IQueryable<SubType>>().Setup(m => m.Expression).Returns(() => { return dbSet.OfType<SubType>().Expression; });
        mockSet.As<IQueryable<SubType>>().Setup(m => m.ElementType).Returns(() => { return dbSet.OfType<SubType>().ElementType; });
        mockSet.As<IQueryable<SubType>>().Setup(m => m.GetEnumerator()).Returns(() => { return dbSet.OfType<SubType>().GetEnumerator(); });

        mockSet.Setup(m => m.Add(It.IsAny<SubType>())).Returns<SubType>(i => { dbSet.Add(i); return i; });
        mockSet.Setup(m => m.AddRange(It.IsAny<IEnumerable<SubType>>())).Returns<IEnumerable<SubType>>((i) => { dbSet.AddRange(i); return i; });
        mockSet.Setup(m => m.Remove(It.IsAny<SubType>())).Returns<SubType>(i => { dbSet.Remove(i); return i; });
        mockSet.As<IDbSet<SubType>>().Setup(m => m.Find(It.IsAny<object[]>())).Returns<object[]>((i) => { return dbSet.Find(i) as SubType; });

        baseSet.Setup(m => m.Create<SubType>()).Returns(() => { return mockSet.Object.Create(); });

        db.Setup(x => x.Set<SubType>()).Returns(mockSet.Object);
        return mockSet;
    }
}

Answer 3

Microsoft published a very well explained guide providing an in-memory implementation of DbSet which has a complete implemention for all the methods on DbSet.

Check the article at http://msdn.microsoft.com/en-us/data/dn314431.aspx#doubles