如何在委托上模拟异常以测试MVC Filter的特定分支

要触发ActionFilter里的else分支，核心是让next()执行后返回的ActionExecutedContext包含非空的Exception属性，有两种简单实现方式：

方式一：直接构造带异常的ActionExecutedContext #

修改你的MockDelegate，返回一个已经设置了Exception的ActionExecutedContext实例：

Task<ActionExecutedContext> MockDelegate() => Task.FromResult( 
    new ActionExecutedContext(executionContext.ActionContext, null, null!)
    {
        Exception = new InvalidOperationException("模拟业务操作异常")
    });

方式二：让MockDelegate直接抛出异常 #

也可以让next委托在执行时直接抛出异常，Asp.Net Core框架会自动将其包装成带异常的ActionExecutedContext：

Task<ActionExecutedContext> MockDelegate() => throw new InvalidOperationException("模拟业务操作异常");

修改后的完整测试代码 #

这里用方式一的实现为例，替换原代码中的MockDelegate即可：

public async Task ExecuteControllerOperation_EXCEPTION_IN_OPERATION_Success()
{
    //arrange
    var actionFilter = new TransactionSupportActionFilter();
    var executionContext = CreateDefaultActionContext(new List<string>());

    // 修改MockDelegate，返回带异常的上下文
    Task<ActionExecutedContext> MockDelegate() => Task.FromResult( 
                new ActionExecutedContext(executionContext.ActionContext, null, null!)
                {
                    Exception = new InvalidOperationException("模拟业务操作抛出的异常")
                });

    var actionExecutingContext = new ActionExecutingContext(
                executionContext.ActionContext,
                new List<IFilterMetadata>(),
                new Dictionary<string, object>(),
                controller: null!);

    //act
    await actionFilter.OnActionExecutionAsync(actionExecutingContext, MockDelegate);

    //assert
    Assert.True(executionContext.HttpContext.Response.Headers.ContainsKey(HttpHeaderKey), "Missing header");
    Assert.True(executionContext.HttpContext.Response.Headers[HttpHeaderKey].ToString() == Other, $"Expecting {Other} type");
}

这样修改后，ActionFilter中的result.Exception就会不为null，自然会进入你要测试的else分支。

内容的提问来源于stack exchange，提问作者advapi