单元测试中使用Moq对EF的DbSet进行mock

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).
上一篇:Django 自带登录验证:authenticate和login,login_require,logout模块


下一篇:【转】包管理器Bower详细讲解