MongoDB returns IAsyncCursor 的 C# 驱动程序 Mock 方法

Question

我正在为使用 mongoDB c# 驱动程序的 DAL 创建一些单元测试。问题是我有这个方法要测试：

    public async virtual Task<IEnumerable<T>> GetAsync(Expression<Func<T, bool>> predicate)
    {
        return (await Collection.FindAsync(predicate)).ToList();
    }

并使用 Moq 我已经像这样模拟了这个集合：

var mockMongoCollectionAdapter = new Mock<IMongoCollectionAdapter<Entity>>();

var expectedEntities = new List<Entity>
{
    mockEntity1.Object,
    mockEntity2.Object
};

mockMongoCollectionAdapter.Setup(x => x.FindAsync(It.IsAny<Expression<Func<Entity,bool>>>(), null, default(CancellationToken))).ReturnsAsync(expectedEntities as IAsyncCursor<Entity>);

但由于 expectedEntities as IAsyncCursor<Entity> 为 null，因此测试无效。

模拟此方法和处理 IAsyncCursor 的最佳方法是什么？

Answer 1

模拟 IAsyncCursor<TDocument> interface 以便它可以被枚举。反正接口上的方法不多

var mockCursor = new Mock<IAsyncCursor<Entity>>();
mockCursor.Setup(_ => _.Current).Returns(expectedEntities); //<-- Note the entities here
mockCursor
    .SetupSequence(_ => _.MoveNext(It.IsAny<CancellationToken>()))
    .Returns(true)
    .Returns(false);
mockCursor
    .SetupSequence(_ => _.MoveNextAsync(It.IsAny<CancellationToken>()))
    .Returns(Task.FromResult(true))
    .Returns(Task.FromResult(false));

mockMongoCollectionAdapter
    .Setup(x => x.FindAsync(
            It.IsAny<Expression<Func<Entity, bool>>>(),
            null,
            It.IsAny<CancellationToken>()
        ))
    .ReturnsAsync(mockCursor.Object); //<-- return the cursor here.

有关如何枚举游标的参考，请查看此答案。

在此之后，您将能够理解为什么要为 mock 设置 move next 方法的序列。

Answer 2

如果它对其他人有帮助....根据@Nkosi 的嘲讽回答，我实现了以下 class

public class MockAsyncCursor<T> : IAsyncCursor<T>
{
    private readonly IEnumerable<T> _items;
    private bool called = false;

    public MockAsyncCursor(IEnumerable<T> items)
    {
        _items = items ?? Enumerable.Empty<T>();
    }

    public IEnumerable<T> Current => _items;

    public bool MoveNext(CancellationToken cancellationToken = new CancellationToken())
    {
        return !called && (called = true);
    }

    public Task<bool> MoveNextAsync(CancellationToken cancellationToken)
    {
        return Task.FromResult(MoveNext(cancellationToken));
    }

    public void Dispose()
    {
    }
}

MongoDB returns IAsyncCursor 的 C# 驱动程序 Mock 方法

MongoDB C# driver Mock method that returns IAsyncCursor

c#

unit-testing

moq

mongodb

mongodb-.net-driver