刚用上Moq，就用它解决了一个IUnitOfWork的mock问题，在这篇博文中记录一下。
开发场景
Application服务层BlogCategoryService的实现代码如下：
public class BlogCategoryService : IBlogCategoryService
{
private IBlogCategoryRepository _blogCategoryRepository;
public BlogCategoryServiceImp(IBlogCategoryRepository blogCategoryRepository)
{
_blogCategoryRepository = blogCategoryRepository;
}
public async Task<IList<BlogCategory>> GetCategoriesAsync(int blogId)
{
return await _blogCategoryRepository.GetCategories(blogId).ToListAsync();
}
}
这里用到了Entity Framework中System.Data.Entity命名空间下的ToListAsync()扩展方法。
Repository层BlogCategoryRepository的实现代码如下：
public class BlogCategoryRepository : IBlogCategoryRepository
{
private IQueryable<BlogCategory> _categories;
public BlogCategoryRepository(IUnitOfWork unitOfWork)
{
_categories = unitOfWork.Set<BlogCategory>();
}
public IQueryable<BlogCategory> GetCategories(int blogId)
{
return _categories.Where(c => c.BlogId == blogId);
}
}
这里在BlogCategoryRepository的构造函数中通过IUnitOfWork接口获取BlogCategory的数据集。
在单元测试中一开始是这样用Moq对IUnitOfWork接口进行mock的——让IUnitOfWork.Set()方法直接返回IQueryable类型的BlogCategory集合，代码如下：
[Fact]
public async Task GetCategoriesTest()
{
var blogCategories = new List<BlogCategory>()
{
new BlogCategory { BlogId = 1, Active = true, CategoryId = 1, Title = "C#" },
new BlogCategory { BlogId = 1, Active = false, CategoryId = 2, Title = "ASP.NET Core" }
}.AsQueryable();
var mockUnitOfWork = new Mock<IUnitOfWork>();
mockUnitOfWork.Setup(u => u.Set<BlogCategory>()).Returns(blogCategories);
_categoryService = new BlogCategoryServiceImp(new BlogCategoryRepository(mockUnitOfWork.Object));
var actual = await _categoryService.GetCategoriesAsync(1);
Assert.Equal(2, actual.Count());
actual.ToList().ForEach(c => Assert.Equal(1, c.BlogId));
}
遇到问题
运行单元测试时，却出现下面的错误：
The source IQueryable doesn't implement IDbAsyncEnumerable<BlogCategory>.
Only sources that implement IDbAsyncEnumerable can be used for Entity Framework asynchronous operations.
出现这个错误是由于在BlogCategoryService中用到了EF的ToListAsync()扩展方法，使用这个扩展方法需要实现IDbAsyncEnumerable相关接口，而通过List转换过来的IQueryable并没有实现这个接口。要解决这个问题，我们需要使用实现IDbAsyncEnumerable相关接口的集合类型，而EF中已经天然内置了这样的集合类型，它就是DbSet。只要能mock出DbSet，问题就迎刃而解。
解决问题
那如何mock呢？比想象中复杂得多，幸好在msdn网站上发现了现成的mock实现代码（详见 Testing with a mocking framework ），照此就可以轻松mock。
mock之前需要实现这三个接口：IDbAsyncEnumerator，IDbAsyncEnumerable，IDbAsyncQueryProvider 。
1）TestDbAsyncEnumerator 实现 IDbAsyncEnumerator
public 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; }
}
}
2）TestDbAsyncEnumerable 实现 IDbAsyncEnumerable
public class TestDbAsyncEnumerable<T> : EnumerableQuery<T>, IDbAsyncEnumerable<T>, IQueryable<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();
}
IQueryProvider IQueryable.Provider
{
get { return new TestDbAsyncQueryProvider<T>(this); }
}
}
3）TestDbAsyncQueryProvider 实现 IDbAsyncQueryProvider
public class TestDbAsyncQueryProvider<TEntity> : IDbAsyncQueryProvider
{
private readonly IQueryProvider _inner;
public 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));
}
}
然后将之前的mock代码：
var mockUnitOfWork = new Mock<IUnitOfWork>();
mockUnitOfWork.Setup(u => u.Set<BlogCategory>()).Returns(blogCategories);
改为下面的代码：
#region mockSet
var mockSet = new Mock<DbSet<BlogCategory>>();
mockSet.As<IDbAsyncEnumerable<BlogCategory>>()
.Setup(m => m.GetAsyncEnumerator())
.Returns(new TestDbAsyncEnumerator<BlogCategory>(blogCategories.GetEnumerator()));
mockSet.As<IQueryable<BlogCategory>>()
.Setup(m => m.Provider)
.Returns(new TestDbAsyncQueryProvider<BlogCategory>(blogCategories.Provider));
mockSet.As<IQueryable<BlogCategory>>().Setup(m => m.Expression).Returns(blogCategories.Expression);
mockSet.As<IQueryable<BlogCategory>>().Setup(m => m.ElementType).Returns(blogCategories.ElementType);
mockSet.As<IQueryable<BlogCategory>>().Setup(m => m.GetEnumerator()).Returns(blogCategories.GetEnumerator());
#endregion
var mockUnitOfWork = new Mock<IUnitOfWork>();
mockUnitOfWork.Setup(u => u.Set<BlogCategory>()).Returns(mockSet.Object);
这样成功mock出DbSet之后，单元测试成功通过，问题就解决了。
1 passed, 0 failed, 0 skipped, took 2.75 seconds (xUnit.net 1.9.2 build 1705).