How do you mock adding items to a repository or DbContext using moq? - entity-framework

Question

The examples I've seen for using moq for a repository only show how to mock things being returned. I have a somewhat strange requirement: when a query is executed, if a condition exists, a certain item should be added to the repository. I am wondering how to test this without querying the database. I know how to mock the condition existing, but then how do you setup the mock so that you can test that the certain item is added?

Answer 1

Try to use fake in memory repository instead of moq, for example universal generic repository for all entities:
public interface IInMemoryRepository<T> where T : class
{
IQueryable<T> GetAll();
void Create(T item);
void Update(T item);
T GetItem(Expression<Func<T, bool>> expression);
void Delete(T item);
}
public class InMemoryRepository<T> : IInMemoryRepository<T> where T : class
{
private int _incrementer = 0;
public Dictionary<int, T> List = new Dictionary<int, T>();
public IQueryable<T> GetAll()
{
return List.Select(x => x.Value).AsQueryable();
}
public void Create(T item)
{
_incrementer++;
item.GetType().GetProperties().First(p => p.Name == "Id").SetValue(item, _incrementer, null);
List.Add(_incrementer, item);
}
public void Update(T item)
{
var key = (int)item.GetType().GetProperties().First(p => p.Name == "Id").GetValue(item, null);
List[key] = item;
}
public T GetItem(Expression<Func<T, bool>> expression)
{
return List.Select(x => x.Value).SingleOrDefault(expression.Compile());
}
public void Delete(T item)
{
var key = (int)item.GetType().GetProperties().First(p => p.Name == "Id").GetValue(item, null);
List.Remove(key);
}
}

Answer 2

You would not mock the repository; you would have an alternate repository that would use an in-memory store instead of the database, then use IoC to select the correct repository implementation for tests/code.

Answer 3

This blog article might be of use, although my design has changed somewhat since I wrote the post and I really need to update it. I used teh generic repository pattern in a way that enables the DbContext to be mocked. This allows the data access layer to be tested 'right up to the edges'.

Answer 4

Times have changed -- since the release of Entity Framework 6 it has become much easier to mock database context and datasets. This article outlines the particulars.
Testing non-query scenarios
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;
using System.Data.Entity;
namespace TestingDemo
{
[TestClass]
public class NonQueryTests
{
[TestMethod]
public void CreateBlog_saves_a_blog_via_context()
{
var mockSet = new Mock<DbSet<Blog>>();
var mockContext = new Mock<BloggingContext>();
mockContext.Setup(m => m.Blogs).Returns(mockSet.Object);
var service = new BlogService(mockContext.Object);
service.AddBlog("ADO.NET Blog", "http://blogs.msdn.com/adonet");
mockSet.Verify(m => m.Add(It.IsAny<Blog>()), Times.Once());
mockContext.Verify(m => m.SaveChanges(), Times.Once());
}
}
}
Testing query scenarios
Query testing is pretty sweet now, because you can build up test data sets in code and then execute your tests against them:
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
namespace TestingDemo
{
[TestClass]
public class QueryTests
{
[TestMethod]
public void GetAllBlogs_orders_by_name()
{
var data = new List<Blog>
{
new Blog { Name = "BBB" },
new Blog { Name = "ZZZ" },
new Blog { Name = "AAA" },
}.AsQueryable();
var mockSet = new Mock<DbSet<Blog>>();
mockSet.As<IQueryable<Blog>>().Setup(m => m.Provider).Returns(data.Provider);
mockSet.As<IQueryable<Blog>>().Setup(m => m.Expression).Returns(data.Expression);
mockSet.As<IQueryable<Blog>>().Setup(m => m.ElementType).Returns(data.ElementType);
mockSet.As<IQueryable<Blog>>().Setup(m => m.GetEnumerator()).Returns(0 => data.GetEnumerator());
var mockContext = new Mock<BloggingContext>();
mockContext.Setup(c => c.Blogs).Returns(mockSet.Object);
var service = new BlogService(mockContext.Object);
var blogs = service.GetAllBlogs();
Assert.AreEqual(3, blogs.Count);
Assert.AreEqual("AAA", blogs[0].Name);
Assert.AreEqual("BBB", blogs[1].Name);
Assert.AreEqual("ZZZ", blogs[2].Name);
}
}
}

Answer 5

You can do this by mocking the DbSet.Add() method, like so:
[Fact]
public void CreateBlog_saves_a_blog_via_context()
{
var data = new List<Blog>
{
new Blog { Name = "BBB" },
new Blog { Name = "ZZZ" },
new Blog { Name = "AAA" },
};
var mockSet = new Mock<DbSet<Blog>>();
mockSet.Setup(blogs => blogs.Add(It.IsAny<Blog>)).Returns<Blog>(blog =>
{
data.Add(blog);
return blog;
});
var mockContext = new Mock<BloggingContext>();
mockContext.Setup(m => m.Blogs).Returns(mockSet.Object);
var service = new BlogService(mockContext.Object);
var blog = service.AddBlog("_ADO.NET Blog", "http://blogs.msdn.com/adonet");
var blogs = service.GetAllBlogs();
mockSet.Verify(m => m.Add(It.IsAny<Blog>()), Times.Once());
mockContext.Verify(m => m.SaveChanges(), Times.Once());
Assert.NotNull(blog)
Assert.Equal(4, blogs.Count);
Assert.Equal("AAA", blogs(1).Name);
Assert.Equal("BBB", blogs(2).Name);
Assert.Equal("ZZZ", blogs(3).Name);
}
This is adapted from the documentation found here.