[release/7.0-rc2] Use determinism instead of timing in cancellation t…

…ests (#75655)

* Use determinism instead of timing in cancellation tests

* Add an explanatory comment to the test.

* Spell "canceling" with only one L.

Co-authored-by: Jeremy Barton <jbarton@microsoft.com>

src/libraries/System.Security.Cryptography/tests/HashAlgorithmTest.cs

@@ -62,19 +62,27 @@ public async Task VerifyComputeHashAsync(int size)
  [ActiveIssue("https://github.com/dotnet/runtime/issues/37669", TestPlatforms.Browser)]
  public async Task ComputeHashAsync_SupportsCancellation()
  {
- using (CancellationTokenSource cancellationSource = new CancellationTokenSource(100))
- using (PositionValueStream stream = new SlowPositionValueStream(10000))
+ using (CancellationTokenSource cancellationSource = new CancellationTokenSource())
+ using (PositionValueStream stream = new SelfCancelingStream(10000, cancellationSource))
  using (HashAlgorithm hash = new SummingTestHashAlgorithm())
  {
+ // The stream has a length longer than ComputeHashAsync's read buffer,
+ // so ReadAsync will get called multiple times.
+ // The first call succeeds, but moves the cancellation source to canceled,
+ // and the second call then fails with an OperationCanceledException, canceling the
+ // whole operation.
  await Assert.ThrowsAnyAsync<OperationCanceledException>(
  () => hash.ComputeHashAsync(stream, cancellationSource.Token));
+
+ Assert.True(cancellationSource.IsCancellationRequested);
  }
  }
 
  [Fact]
  public void ComputeHashAsync_Disposed()
  {
- using (PositionValueStream stream = new SlowPositionValueStream(10000))
+ using (CancellationTokenSource cancellationSource = new CancellationTokenSource())
+ using (PositionValueStream stream = new SelfCancelingStream(10000, cancellationSource))
  using (HashAlgorithm hash = new SummingTestHashAlgorithm())
  {
  hash.Dispose();
@@ -85,6 +93,10 @@ public void ComputeHashAsync_Disposed()
  // Not returning or awaiting the Task, it never got created.
  hash.ComputeHashAsync(stream);
  });
+
+ // If SelfCancelingStream.Read (or ReadAsync) was called it will trip cancellation,
+ // so use that as a signal for whether or not the stream was ever read from.
+ Assert.False(cancellationSource.IsCancellationRequested, "Stream.Read was invoked");
  }
  }
 
@@ -123,15 +135,19 @@ protected override void HashCore(byte[] array, int ibStart, int cbSize)
  // implementations by verifying the right value is produced.
  }
 
- private class SlowPositionValueStream : PositionValueStream
+ private class SelfCancelingStream : PositionValueStream
  {
- public SlowPositionValueStream(int totalCount) : base(totalCount)
+ private readonly CancellationTokenSource _cancellationSource;
+
+ public SelfCancelingStream(int totalCount, CancellationTokenSource cancellationSource)
+ : base(totalCount)
  {
+ _cancellationSource = cancellationSource;
  }
 
  public override int Read(byte[] buffer, int offset, int count)
  {
- System.Threading.Thread.Sleep(1000);
+ _cancellationSource.Cancel(throwOnFirstException: true);
  return base.Read(buffer, offset, count);
  }
  }