单元测试睡眠持续时间 polly 等待重试策略

Question

我想编写一个单元测试来查看执行是否在指定的持续时间内处于休眠状态。 我遇到了属于Polly.Utilities<\/code>的SystemClock<\/code> ，但我正在寻找类似于此处WaitAndRetrySpecs<\/code><\/a> Polly 单元测试的实现WaitAndRetrySpecs<\/code><\/a> ，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);
  }

Answer 1

您可以通过使用onRetry函数来实现这一点。

为了简单IsTransientError ，让我定义IsTransientError和GetSleepDurationByRetryAttempt方法，如下所示：

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 来缩短您的策略定义：

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

所以，回到 onRetry。 有一个具有以下签名的重载： Action<Exception, TimeSpan, Context> 。 这里的第二个参数是睡眠持续时间。

我们需要做的就是在这里提供一个函数，它可以累积睡眠时长。

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

让我们把所有这些放在一起：

[Fact]
public async Task GivenACustomSleepDurationProvider_WhenIUseItInARetryPolicy_ThenTheAccumulatedDurationIsAsExpected()
{
    //Arrange
    var totalSleepDuration = TimeSpan.Zero;
    var customPolicy = Policy
        .Handle<SqlException>(IsTransientError)
        .WaitAndRetryAsync(3, GetSleepDurationByRetryAttempt,
            onRetry: (ex, duration, 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 ：减少延误并介绍理论

根据您的要求，使用不同的参数运行相同的测试用例可能是有意义的。 这就是Theory和InlineData可以帮助您的地方：

[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, GetSleepDurationByRetryAttempt,
            onRetry: (ex, duration, 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

为了使TimeSpan的传输和检索更加类型安全，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 Policy 创建逻辑：

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

现在让我们把所有这些放在一起（再一次）：

[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 = 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);
}

Answer 2

测试不起作用，因为您使用的是 WaitAndRetryAsync 而不是 WaitAndRetry。 我有一个类似的问题并通过使用修复

 SystemClock.SleepAsync = (s, cts) =>
        {
            totalTimeSlept += s.Seconds;
            return Task.CompletedTask;
        };