我有以下方法:
public static async Task<bool> CreateIfNotExistsAsync(
this ISegment segment,
CancellationToken cancellationToken)
{
Requires.ArgNotNull(segment, nameof(segment));
try
{
await segment.CreateAsync(cancellationToken);
return true;
}
catch (Exception error)
{
if (error.CanSuppress() && !cancellationToken.IsCancellationRequested)
{
var status = await segment.GetStatusAsync(cancellationToken);
if (status.Exists)
{
return false;
}
}
throw;
}
}
...我已经编写了应该涵盖所有块的测试。然而;代码覆盖率结果(在Visual Studio 2015 Update 3中)显示没有覆盖两个块:
我认为这与在catch块中为await
生成的代码有关,所以我尝试重写这样的方法:
public static async Task<bool> CreateIfNotExistsAsync(
this ISegment segment,
CancellationToken cancellationToken)
{
Requires.ArgNotNull(segment, nameof(segment));
ExceptionDispatchInfo capturedError;
try
{
await segment.CreateAsync(cancellationToken);
return true;
}
catch (Exception error)
{
if (error.CanSuppress() && !cancellationToken.IsCancellationRequested)
{
capturedError = ExceptionDispatchInfo.Capture(error);
}
else
{
throw;
}
}
var status = await segment.GetStatusAsync(cancellationToken);
if (!status.Exists)
{
capturedError.Throw();
}
return false;
}
但是,仍然有一个块未被覆盖:
是否可以重写此方法以便完全覆盖它?
以下是我的相关测试:
[TestMethod]
public async Task Create_if_not_exists_returns_true_when_create_succeed()
{
var mock = new Mock<ISegment>();
Assert.IsTrue(await mock.Object.CreateIfNotExistsAsync(default(CancellationToken)));
mock.Verify(_ => _.CreateAsync(It.IsAny<CancellationToken>()), Times.Once);
}
[TestMethod]
public async Task Create_if_not_exists_throws_when_create_throws_and_cancellation_is_requested()
{
var mock = new Mock<ISegment>();
var exception = new Exception();
mock.Setup(_ => _.CreateAsync(It.IsAny<CancellationToken>())).Throws(exception);
try
{
await mock.Object.CreateIfNotExistsAsync(new CancellationToken(true));
Assert.Fail();
}
catch (Exception caught)
{
Assert.AreSame(exception, caught);
}
mock.Verify(_ => _.CreateAsync(It.IsAny<CancellationToken>()), Times.Once);
mock.Verify(_ => _.GetStatusAsync(It.IsAny<CancellationToken>()), Times.Never);
}
[TestMethod]
public async Task Create_if_not_exists_throws_when_create_throws_non_suppressable_exception()
{
var mock = new Mock<ISegment>();
var exception = new OutOfMemoryException();
mock.Setup(_ => _.CreateAsync(It.IsAny<CancellationToken>())).Throws(exception);
try
{
await mock.Object.CreateIfNotExistsAsync(default(CancellationToken));
Assert.Fail();
}
catch (Exception caught)
{
Assert.AreSame(exception, caught);
}
mock.Verify(_ => _.CreateAsync(It.IsAny<CancellationToken>()), Times.Once);
mock.Verify(_ => _.GetStatusAsync(It.IsAny<CancellationToken>()), Times.Never);
}
[TestMethod]
public async Task Create_if_not_exists_throws_when_create_throws_and_status_says_segment_doesnt_exists()
{
var mock = new Mock<ISegment>();
var exception = new Exception();
mock.Setup(_ => _.CreateAsync(It.IsAny<CancellationToken>())).Throws(exception);
mock.Setup(_ => _.GetStatusAsync(It.IsAny<CancellationToken>()))
.ReturnsAsync(new SegmentStatus(false, false, null, 0));
try
{
await mock.Object.CreateIfNotExistsAsync(default(CancellationToken));
Assert.Fail();
}
catch (Exception caught)
{
Assert.AreSame(exception, caught);
}
mock.Verify(_ => _.CreateAsync(It.IsAny<CancellationToken>()), Times.Once);
mock.Verify(_ => _.GetStatusAsync(It.IsAny<CancellationToken>()), Times.Once);
}
[TestMethod]
public async Task Create_if_not_exists_returns_false_when_create_throws_and_status_says_segment_exists()
{
var mock = new Mock<ISegment>();
mock.Setup(_ => _.CreateAsync(It.IsAny<CancellationToken>())).Throws<Exception>();
mock.Setup(_ => _.GetStatusAsync(It.IsAny<CancellationToken>()))
.ReturnsAsync(new SegmentStatus(true, false, null, 0));
Assert.IsFalse(await mock.Object.CreateIfNotExistsAsync(default(CancellationToken)));
mock.Verify(_ => _.CreateAsync(It.IsAny<CancellationToken>()), Times.Once);
mock.Verify(_ => _.GetStatusAsync(It.IsAny<CancellationToken>()), Times.Once);
}
这是CanSuppress
- 逻辑:
private static readonly Exception[] EmptyArray = new Exception[0];
/// <summary>
/// Determines whether an <see cref="Exception"/> can be suppressed.
/// </summary>
/// <param name="exception">
/// The <see cref="Exception"/> to test.
/// </param>
/// <returns>
/// <c>true</c> when <paramref name="exception"/> can be suppressed; otherwise <c>false</c>.
/// </returns>
/// <remarks>
/// <para>
/// We do not want to suppress <see cref="OutOfMemoryException"/> or <see cref="ThreadAbortException"/>
/// or any exception derived from them (except for <see cref="InsufficientMemoryException"/>, which we
/// do allow suppression of).
/// </para>
/// <para>
/// An exception that is otherwise suppressable is not considered suppressable when it has a nested
/// non-suppressable exception.
/// </para>
/// </remarks>
public static bool CanSuppress(this Exception exception)
{
foreach (var e in exception.DescendantsAndSelf())
{
if ((e is OutOfMemoryException && !(e is InsufficientMemoryException)) ||
e is ThreadAbortException)
{
return false;
}
}
return true;
}
private static IEnumerable<Exception> DescendantsAndSelf(this Exception exception)
{
if (exception != null)
{
yield return exception;
foreach (var child in exception.Children().SelectMany(ExceptionExtensions.DescendantsAndSelf))
{
yield return child;
}
}
}
private static IEnumerable<Exception> Children(this Exception parent)
{
DebugAssumes.ArgNotNull(parent, nameof(parent));
var aggregate = parent as AggregateException;
if (aggregate != null)
{
return aggregate.InnerExceptions;
}
else if (parent.InnerException != null)
{
return new[] { parent.InnerException };
}
else
{
return ExceptionExtensions.EmptyArray;
}
}
答案 0 :(得分:3)
好吧 - 经过大量的挖掘 - 罪魁祸首是await segment.GetStatusAsync(cancellationToken)
。这会导致代码覆盖率在部分覆盖时查看throw
。使用非异步方法替换该行正确显示throw
被覆盖
现在,async
在内部创建了一个状态机。你可以在代码覆盖中看到这个,它找到一个名为
<CreateIfNotExistsAsync>d__1.MoveNext:
在生成的IL中, this 弹出给我:
IL_01B4: ldfld MyExtensions+<CreateIfNotExistsAsync>d__1.<>s__1
IL_01B9: isinst System.Exception
IL_01BE: stloc.s 0A
IL_01C0: ldloc.s 0A
IL_01C2: brtrue.s IL_01CB
IL_01C4: ldarg.0
IL_01C5: ldfld MyExtensions+<CreateIfNotExistsAsync>d__1.<>s__1
IL_01CA: throw
IL_01CB: ldloc.s 0A
IL_01CD: call System.Runtime.ExceptionServices.ExceptionDispatchInfo.Capture
IL_01D2: callvirt System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw
在这里,有两种方法抛出异常:
IL_01B4: ldfld MyExtensions+<CreateIfNotExistsAsync>d__1.<>s__1
IL_01B9: isinst System.Exception
IL_01BE: stloc.s 0A
IL_01C0: ldloc.s 0A
IL_01C2: brtrue.s IL_01CB
IL_01C4: ldarg.0
IL_01C5: ldfld MyExtensions+<CreateIfNotExistsAsync>d__1.<>s__1
IL_01CA: throw
这实际上取自s__1
的字段,并检查它是否为Exception
类型。例如:machine.state1 is Exception
然后,如果是,则分支到IL_01CB
IL_01CB: ldloc.s 0A
IL_01CD: call System.Runtime.ExceptionServices.ExceptionDispatchInfo.Capture
IL_01D2: callvirt System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw
抛出异常。但是,如果它是 false ,它会调用throw
OpCode。
这意味着throw
被转换为两条可能的路径,其中只有一条路径被执行。我不确定C#中IL_01B9: isinst System.Exception
是否可能是假的,但我可能错了 - 或者在.NET中可能是错的。
坏消息是,我没有解决方案。我的建议是:使用代码覆盖率作为指南,因为即使100%的覆盖率也不意味着代码没有错误。话虽如此,您可以逻辑推断throw
被标记为“部分覆盖”,与完全覆盖的内容基本相同