异步方法返回 null

本文介绍了异步方法返回 null的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

如果我尝试模拟包含 async 方法的类型，例如:

If I try to mock a type containing an async method such as :

interface Foo { Task<int> Bar(); }

然后 mock 的 Bar 方法返回 null.我猜 Moq 选择 default(Task<int>) 作为我的方法的默认返回值，这确实是 null.然而，起订量应该选择像 Task.FromResult(default(int)) 这样的东西作为默认值.我可以强制 Moq 使异步方法返回非空任务吗?

Then the mock's Bar method is returning null. I guess Moq is choosing default(Task<int>) as default return value for my method, which is indeed null. However Moq should rather choose something like Task.FromResult(default(int)) as default value. Can I force Moq to make async methods returning non-null Tasks ?

推荐答案

如果有人感兴趣，我做了一个扩展类，它可以让异步方法不那么冗长:

If someone is interested, I made an extension class which makes async methods stubing less verbose :

public static class SetupExtensions { public static IReturnsResult<TMock> ReturnsTask<TMock, TResult>( this ISetup<TMock, Task<TResult>> setup) where TMock : class { return setup.Returns(() => Task.FromResult(default(TResult))); } public static IReturnsResult<TMock> ReturnsTask<TMock, TResult>( this ISetup<TMock, Task<TResult>> setup, TResult value) where TMock : class { return setup.Returns(() => Task.FromResult(value)); } public static IReturnsResult<TMock> ReturnsTask<TMock, TResult>( this ISetup<TMock, Task<TResult>> setup, Func<TResult> func) where TMock : class { return setup.Returns(Task.Factory.StartNew(func)); } public static IReturnsResult<TMock> ReturnsTask<TMock, T, TResult>( this ISetup<TMock, Task<TResult>> setup, Func<T, TResult> func) where TMock : class { return setup.Returns<T>(arg => Task.Factory.StartNew(() => func(arg))); } public static IReturnsResult<TMock> ReturnsTask<TMock, T1, T2, TResult>( this ISetup<TMock, Task<TResult>> setup, Func<T1, T2, TResult> func) where TMock : class { return setup.Returns<T1, T2>((arg1, arg2) => Task.Factory.StartNew(() => func(arg1, arg2))); } public static IReturnsResult<TMock> ReturnsTask<TMock, T1, T2, T3, TResult>( this ISetup<TMock, Task<TResult>> setup, Func<T1, T2, T3, TResult> func) where TMock : class { return setup.Returns<T1, T2, T3>((arg1, arg2, arg3) => Task.Factory.StartNew(() => func(arg1, arg2, arg3))); } public static IReturnsResult<TMock> ReturnsTask<TMock, T1, T2, T3, T4, TResult>( this ISetup<TMock, Task<TResult>> setup, Func<T1, T2, T3, T4, TResult> func) where TMock : class { return setup.Returns<T1, T2, T3, T4>((arg1, arg2, arg3, arg4) => Task.Factory.StartNew(() => func(arg1, arg2, arg3, arg4))); } public static IReturnsResult<TMock> ReturnsTask<TMock>(this ISetup<TMock, Task> setup, Action action) where TMock : class { return setup.Returns(Task.Factory.StartNew(action)); } public static IReturnsResult<TMock> ReturnsTask<TMock, T>(this ISetup<TMock, Task> setup, Action<T> action) where TMock : class { return setup.Returns<T>(arg => Task.Factory.StartNew(() => action(arg))); } public static IReturnsResult<TMock> ReturnsTask<TMock, T1, T2>(this ISetup<TMock, Task> setup, Action<T1, T2> action) where TMock : class { return setup.Returns<T1, T2>((arg1, arg2) => Task.Factory.StartNew(() => action(arg1, arg2))); } public static IReturnsResult<TMock> ReturnsTask<TMock, T1, T2, T3>(this ISetup<TMock, Task> setup, Action<T1, T2, T3> action) where TMock : class { return setup.Returns<T1, T2, T3>((arg1, arg2, arg3) => Task.Factory.StartNew(() => action(arg1, arg2, arg3))); } public static IReturnsResult<TMock> ReturnsTask<TMock, T1, T2, T3, T4>(this ISetup<TMock, Task> setup, Action<T1, T2, T3, T4> action) where TMock : class { return setup.Returns<T1, T2, T3, T4>((arg1, arg2, arg3, arg4) => Task.Factory.StartNew(() => action(arg1, arg2, arg3, arg4))); } public static IReturnsResult<TMock> ReturnsTask<TMock>(this ISetup<TMock, Task> setup) where TMock : class { return setup.Returns(Task.Factory.StartNew(delegate { })); } }

一些例子:

//Example 1 : public interface IFoo { Task Bar(); } var mock = new Mock<IFoo>(); mock.Setup(m => m.Bar()).ReturnsTask(); //await Bar() will return void //Example 2 : public interface IFoo { Task<int> Bar(); } var mock = new Mock<IFoo>(); mock.Setup(m => m.Bar()).ReturnsTask(); //await Bar() will return default(int) //Example 3 : public interface IFoo { Task<int> Bar(); } var mock = new Mock<IFoo>(); mock.Setup(m => m.Bar()).ReturnsTask(4); //await Bar() will return 4; //Example 4 : public interface IFoo { Task<int> Bar(int x, int y); } var mock = new Mock<IFoo>(); mock.Setup(m => m.Bar(It.IsAny<int>(), It.IsAny<int>())) .ReturnsTask<IFoo, int, int, int>((x,y) => x + y); //await Bar(x, y) will return x + y;