单元测试睡眠时间Polly等待重试策略

问题描述

我想编写一个单元测试，以查看执行是否在指定的持续时间内处于休眠状态。我遇到了SystemClock的一部分Polly.Utilities，但是我正在寻找类似于此处WaitAndRetrySpecs提到的Polly单元测试的实现，它看起来像这样

 [Fact]
 public void Should_sleep_for_the_specified_duration_each_retry_when_specified_exception_thrown_same_number_of_times_as_there_are_sleep_durations()
 {
      var totalTimeSlept = 0;

      var policy = Policy
            .Handle<DivideByZeroException>()
            .WaitAndRetry(new[]
            {
               1.Seconds(),2.Seconds(),3.Seconds()
            });

      SystemClock.Sleep = span => totalTimeSlept += span.Seconds;

      policy.RaiseException<DivideByZeroException>(3);

      totalTimeSlept.Should()
                      .Be(1 + 2 + 3);
  }

当前我的政策如下

var customPolicy = Policy
                     .Handle<sqlException>(x => IsTransientError(x))
                     .WaitAndRetryAsync(
                      3,(retryAttempt) => getSleepDurationByRetryAtempt(retryAttempt)
                     );

我想测试政策制定的总体时间。对于每次重试尝试[1,2,3]，睡眠时间为[1,3]。在全部3次重试之后，总睡眠时间应为1 + 2 + 3 =6。此测试与上面链接中提到的Polly规格非常相似。

问题：：我如何为customPolicy编写单元测试，以测试类似于Polly规范的总睡眠时间。我想看一个实现或编写单元测试的说明。

解决方法

您可以通过使用onRetry函数来实现此目的。

为简单起见，让我定义如下的IsTransientError和GetSleepDurationByRetryAttempt方法：

public TimeSpan GetSleepDurationByRetryAttempt(int attempt) => TimeSpan.FromSeconds(attempt);
public bool IsTransientError(SqlException ex) => true;

顺便说一句，您可以通过避免（不必要的）匿名lambda来缩短策略定义：

var customPolicy = Policy
    .Handle<SqlException>(IsTransientError)
    .WaitAndRetryAsync(3,GetSleepDurationByRetryAttempt)

因此，回到onRetry。 an overload具有以下签名：Action<Exception,TimeSpan,Context>。这里的第二个参数是睡眠时间。

我们要做的就是在此处提供一个功能，该功能可以累积睡眠时间。

var totalSleepDuration = TimeSpan.Zero;
...
onRetry: (ex,duration,ctx) => { totalSleepDuration = totalSleepDuration.Add(duration); }

我们将所有这些放在一起：

[Fact]
public async Task GivenACustomSleepDurationProvider_WhenIUseItInARetryPolicy_ThenTheAccumulatedDurationIsAsExpected()
{
    //Arrange
    var totalSleepDuration = TimeSpan.Zero;
    var customPolicy = Policy
        .Handle<SqlException>(IsTransientError)
        .WaitAndRetryAsync(3,GetSleepDurationByRetryAttempt,onRetry: (ex,ctx) => { totalSleepDuration = totalSleepDuration.Add(duration); }
        );

    //Act
    Func<Task> actionWithRetry = async() => await customPolicy.ExecuteAsync(() => throw new SqlException());
    
    //Assert
    _ = await Assert.ThrowsAsync<SqlException>(actionWithRetry);
    Assert.Equal(6,totalSleepDuration.Seconds);
}

更新＃1 ：减少延迟并介绍理论

根据您的要求，可能需要使用不同的参数运行相同的测试用例。这是Theory和InlineData可以为您提供帮助的地方：

[Theory]
[InlineData(3,600)]
[InlineData(4,1000)]
[InlineData(5,1500)]
public async Task GivenACustomSleepDurationProvider_WhenIUseItInARetryPolicy_ThenTheAccumulatedDurationIsAsExpected(int retryCount,int expectedTotalSleepInMs)
{
    //Arrange
    var totalSleepDuration = TimeSpan.Zero;
    var customPolicy = Policy
        .Handle<SqlException>(IsTransientError)
        .WaitAndRetryAsync(retryCount,ctx) => { totalSleepDuration = totalSleepDuration.Add(duration); }
        );

    //Act
    Func<Task> actionWithRetry = async () => await customPolicy.ExecuteAsync(() => throw new SqlException());

    //Assert
    _ = await Assert.ThrowsAsync<SqlException>(actionWithRetry);
    Assert.Equal(TimeSpan.FromMilliseconds(expectedTotalSleepInMs),totalSleepDuration);
}

public static TimeSpan GetSleepDurationByRetryAttempt(int attempt) => TimeSpan.FromMilliseconds(attempt * 100);

更新＃2 ：通过Context

传递时间跨度

为了进行TimeSpan a bit more type-safe的传输和检索，我们可以为此创建两个扩展方法：

public static class ContextExtensions
{
    private const string Accumulator = "DurationAccumulator";

    public static Context SetAccumulator(this Context context,TimeSpan durationAccumulator)
    {
        context[Accumulator] = durationAccumulator;
        return context;
    }

    public static TimeSpan? GetAccumulator(this Context context)
    {
        if (!context.TryGetValue(Accumulator,out var ts))
            return null;

        if (ts is TimeSpan accumulator) 
            return accumulator;

        return null;
    }
}

我们还可以提取策略创建逻辑：

private AsyncPolicy GetCustomPolicy(int retryCount)
    => Policy
        .Handle<SqlException>(IsTransientError)
        .WaitAndRetryAsync(retryCount,ctx) =>
            {
                var totalSleepDuration = ctx.GetAccumulator();
                if (!totalSleepDuration.HasValue) return;
                totalSleepDuration = totalSleepDuration.Value.Add(duration);
                ctx.SetAccumulator(totalSleepDuration.Value);
            });

现在让我们将所有这些放在一起（再次）：

[Theory]
[InlineData(3,1500)]
public async Task GivenACustomSleepDurationProvider_WhenIUseItInARetryPolicy_ThenTheAccumulatedDurationIsAsExpected(
        int retryCount,int expectedTotalSleepInMs)
{
    //Arrange
    var totalSleepDuration = TimeSpan.Zero;
    var customPolicy = GetCustomPolicy(retryCount);
    var context = new Context().SetAccumulator(totalSleepDuration);

    //Act
    Func<Task> actionWithRetry = async () => await customPolicy.ExecuteAsync(ctx => throw new SqlException(),context);

    //Assert
    _ = await Assert.ThrowsAsync<SqlException>(actionWithRetry);
    var accumulator = context.GetAccumulator();
    Assert.NotNull(accumulator);
    Assert.Equal(TimeSpan.FromMilliseconds(expectedTotalSleepInMs),accumulator.Value);
}

c#c#mstest mstest nunit nunit nunit polly xunit