如何使用 NSubstitute 模拟 DbContext，然后添加/删除数据

我需要模拟 EFDbContext. I use 这里的方法 https://stackoverflow.com/a/21075569/3959480而且效果很好。

// mock a DbSet
var mockDbSet = Substitute.For<DbSet<Foo>, IQueryable<Foo>>();
var data = new List<Foo>().AsQueryable();
((IQueryable<Foo>)mockDbSet).Provider.Returns(data.Provider);
((IQueryable<Foo>)mockDbSet).Expression.Returns(data.Expression);
((IQueryable<Foo>)mockDbSet).ElementType.Returns(data.ElementType);
((IQueryable<Foo>)mockDbSet).GetEnumerator().Returns(data.GetEnumerator());
// now add it to a mock DbContext
var mockContext = Substitute.For<MyDbContextClass>();
mockContext.Set<Foo>().Returns(mockDbSet);

但是在某些测试中我需要能够调用mockContext.Set<Foo>().Add(someFoo) and mockContext.Set<Foo>().Remove(otherFoo)，以及底层添加/删除逻辑的工作。

我试过这个：

mockDbSet.When(x => x.Add(Arg.Any<Foo>())).Do(x => data.Add(x.Arg<Foo>()));

但它抛出Collection was modified; enumeration operation may not execute.

那么如何实现添加/删除功能呢？

您不想将其添加到集合中。您想要做的是检查它（添加/删除/等）是否被调用以及可能是用什么来调用的。

// arrange - check what it was called with. You place asserts in the body of the `Do` expression. Place this before your call that actually executes the code
mockDbSet.Add(Arg.Do<Foo>(foo =>
{
    Assert.IsNotNull(foo);
    // Assert other properties of foo
}));

// act


// assert. Make sure that it was actually called
mockDbSet.Received(1).Add(Arg.Any<Foo>());

如果你想添加一个Foo在稍后的测试中，您可以保留对List of Foo's.

// mock a DbSet
var mockDbSet = Substitute.For<DbSet<Foo>, IQueryable<Foo>>();
var fooList = new List<Foo>();
var data = fooList.AsQueryable();
// rest of your code unchanged

// add it from the code being tested through the mock dbset
mockDbSet.Add(Arg.Do<Foo>(foo =>
{
    fooList.Add(foo);
    // at this point you have to recreate the added IQueryable
    data = fooList.AsQueryable();
    // rest of code you had to add this to the mockDbSet
}));


// act