Add ITestOutputHelper to MockConsole for visible console output in test failures #5700

Copilot · 2026-01-28T02:49:18Z

Improve Console Output Visibility in CollectCommand Tests

This PR addresses issue #5698 by making console output visible when tests fail.

Changes completed:

Key features:

Intelligent buffering: Accumulates text until complete lines are ready to avoid fragmenting output
Performance optimized: Only processes buffer when incoming text contains newlines
Robust exception handling: Uses case-insensitive comparison to catch InvalidOperationException properly
Backward compatible: Optional parameter means existing tests don't need changes
FlushTestLogging method: Ensures any remaining buffered output is written before assertions
Clean separation: Test logging logic extracted into dedicated helper methods

Result:

Console output including error messages and exceptions is now visible in test output under "Standard Output Messages:", making it much easier to diagnose issues when tests fail.

Original prompt

Can you extend the CollectCommandFunctionalTests and CollectLinuxCommandFunctionalTests to increase visibility on the console output observed whenever there are failures. Currently they're swalled by MockConsole, and so we don't know what exception occurred. See #5698 for an example. There is also a suggestion to inject ITestOutputHelper,

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… CollectCommand tests Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

… handling Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

…ilures Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

mdh1418

@copilot can we also update the ConsoleExporterTests to use the ITestOutputHelper as well

src/tests/Common/MockConsole.cs

…leExporterTests Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Copilot · 2026-01-28T19:22:51Z

@copilot can we also update the ConsoleExporterTests to use the ITestOutputHelper as well

Done in cf2edc3. ConsoleExporterTests now uses ITestOutputHelper with all 16 MockConsole instantiations updated.

Copilot

Pull request overview

This PR improves diagnosability of failing tests by making MockConsole optionally mirror console output to xUnit’s ITestOutputHelper, and updates several test suites to pass the output helper into MockConsole.

Changes:

Added optional ITestOutputHelper plumbing to MockConsole, including line-buffering and an explicit FlushOutput() method.
Updated CollectCommandFunctionalTests, CollectLinuxCommandFunctionalTests, and ConsoleExporterTests to inject ITestOutputHelper and pass it to MockConsole.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/tests/Common/MockConsole.cs	Adds optional xUnit output multiplexing, buffering, and flush integration in assert helpers.
src/tests/dotnet-trace/CollectCommandFunctionalTests.cs	Injects `ITestOutputHelper` and routes console output through `MockConsole`.
src/tests/dotnet-trace/CollectLinuxCommandFunctionalTests.cs	Injects `ITestOutputHelper` and routes console output through `MockConsole` across test cases.
src/tests/dotnet-counters/ConsoleExporterTests.cs	Injects `ITestOutputHelper` and passes it to `MockConsole` for better failure output.

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Copilot · 2026-01-28T23:25:23Z

src/tests/Common/MockConsole.cs

+                catch (InvalidOperationException ex) when (ex.Message.Contains("no currently active test"))
+                {
+                    // ITestOutputHelper.WriteLine throws InvalidOperationException with message
+                    // "There is no currently active test" when called after the test has completed.
+                    // This is expected and can be safely ignored.
+                }


The exception filter is case-sensitive: ex.Message.Contains("no currently active test") will NOT match the message quoted in the comment ("There is no currently active test...") due to casing. This means InvalidOperationException can still escape when writes happen after the test completes. Use a case-insensitive check (e.g., IndexOf(..., StringComparison.OrdinalIgnoreCase) >= 0) or compare against the exact expected message consistently.

Fixed in 61ff689. Changed to use StringComparison.OrdinalIgnoreCase for case-insensitive matching.

Copilot · 2026-01-28T23:25:24Z

src/tests/Common/MockConsole.cs

+                    _outputHelper.WriteLine(_outputBuffer.ToString());
+                    _outputBuffer.Clear();
+                }
+                catch (InvalidOperationException ex) when (ex.Message.Contains("no currently active test"))


Same case-sensitive exception filter issue here: ex.Message.Contains("no currently active test") won’t match "There is no currently active test" due to casing, so FlushOutput() can throw after test completion. Make the match case-insensitive or use the exact message string consistently.

Suggested change

catch (InvalidOperationException ex) when (ex.Message.Contains("no currently active test"))

catch (InvalidOperationException ex) when (ex.Message.Contains("no currently active test", StringComparison.OrdinalIgnoreCase))

Fixed in 61ff689. Changed to use StringComparison.OrdinalIgnoreCase for case-insensitive matching.

mdh1418 · 2026-01-28T23:27:03Z

@copilot apply changes based on the comments in this thread

mdh1418 · 2026-01-28T23:28:45Z

Example outputs when there are failures.

./dotnet.sh test src/tests/dotnet-trace/DotnetTrace.UnitTests.csproj

    /home/mihw/repo/diagnostics/src/tests/dotnet-trace/CollectLinuxCommandFunctionalTests.cs(97): error TESTERROR: 
      Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandFunctionalTests.CollectLinuxCommand_ReportsResolveProcessNameErrors (11ms): Error Message: Assert.Equal() Failure: Values differ
      Expected: 3
      Actual:   2
      Stack Trace:
         at Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandFunctionalTests.CollectLinuxCommand_ReportsResolveProcessNameErrors() in /home/mihw/repo/diagnostics/src/tests/dotnet-trace/CollectLinuxCommandFunctionalTes
      ts.cs:line 97
         at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
         at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)
        Standard Output Messages:
       ==========================================================================================
       The collect-linux verb is a new preview feature and relies on an updated version of the
       .nettrace file format. The latest PerfView release supports these trace files but other
       ways of using the trace file may not work yet. For more details, see the docs at
       https://learn.microsoft.com/dotnet/core/diagnostics/dotnet-trace.
       ==========================================================================================
       [ERROR] System.Exception: MIHW
          at Microsoft.Diagnostics.NETCore.Client.DiagnosticsClient.<GetPublishedProcesses>g__GetAllPublishedProcesses|33_0(String[] files)+MoveNext() in /home/mihw/repo/diagnostics/src/Microsoft.Diagnostics.NETCore.Clien
      t/DiagnosticsClient/DiagnosticsClient.cs:line 441
          at System.Linq.Enumerable.DistinctIterator`1.MoveNext()
          at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
          at Microsoft.Internal.Common.Utils.CommandUtils.FindProcessIdWithName(String name) in /home/mihw/repo/diagnostics/src/Tools/Common/CommandUtils.cs:line 20
          at Microsoft.Internal.Common.Utils.CommandUtils.ResolveProcess(Int32 processId, String name, Int32& resolvedProcessId, String& resolvedProcessName) in /home/mihw/repo/diagnostics/src/Tools/Common/CommandUtils.cs
      :line 107
          at Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandHandler.ProcessSupportsUserEventsIpcCommand(Int32 pid, String processName, Int32& resolvedPid, String& resolvedName, String& detectedRuntimeVersion) in /ho
      me/mihw/repo/diagnostics/src/Tools/dotnet-trace/CommandLine/Commands/CollectLinuxCommand.cs:line 304
          at Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandHandler.CollectLinux(CollectLinuxArgs args) in /home/mihw/repo/diagnostics/src/Tools/dotnet-trace/CommandLine/Commands/CollectLinuxCommand.cs:line 95

./test.sh

      <test name="Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandFunctionalTests.CollectLinuxCommand_Probe_CsvToConsole" type="Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandFunctionalTests" method="CollectLinuxCommand_Probe_CsvToConsole" time="0.0561657" result="Fail">
        <output><![CDATA[==========================================================================================
The collect-linux verb is a new preview feature and relies on an updated version of the
.nettrace file format. The latest PerfView release supports these trace files but other
ways of using the trace file may not work yet. For more details, see the docs at
https://learn.microsoft.com/dotnet/core/diagnostics/dotnet-trace.
==========================================================================================
System.Exception: MIHW
   at Microsoft.Diagnostics.NETCore.Client.DiagnosticsClient.<GetPublishedProcesses>g__GetAllPublishedProcesses|33_0(String[] files)+MoveNext() in /home/mihw/repo/diagnostics/src/Microsoft.Diagnostics.NETCore.Client/DiagnosticsClient/DiagnosticsClient.cs:line 441
   at System.Linq.Enumerable.DistinctIterator`1.MoveNext()
   at Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandHandler.SupportsCollectLinux(CollectLinuxArgs args) in /home/mihw/repo/diagnostics/src/Tools/dotnet-trace/CommandLine/Commands/CollectLinuxCommand.cs:line 229
]]></output>
        <failure exception-type="Xunit.Sdk.EqualException">
          <message><![CDATA[Assert.Equal() Failure: Values differ\nExpected: 0\nActual:   5]]></message>
          <stack-trace><![CDATA[   at Microsoft.Diagnostics.Tools.Trace.CollectLinuxCommandFunctionalTests.CollectLinuxCommand_Probe_CsvToConsole() in /home/mihw/repo/diagnostics/src/tests/dotnet-trace/CollectLinuxCommandFunctionalTests.cs:line 140
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)]]></stack-trace>
        </failure>
      </test>

Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Copilot · 2026-01-28T23:34:24Z

@copilot apply changes based on the comments in this thread

Applied the suggested changes in 61ff689. Both exception filters now use case-insensitive comparison with StringComparison.OrdinalIgnoreCase.

noahfalk · 2026-01-29T01:32:18Z

src/tests/Common/MockConsole.cs

        }
        public override void Write(string text)
        {
+            if (_outputHelper != null && !string.IsNullOrEmpty(text))


@copilot - please factor this new code out into a helper function such as BufferTestLogging

Done in a518e4c. Extracted the test logging buffer logic into a BufferTestLogging helper method.

noahfalk · 2026-01-29T01:33:13Z

src/tests/Common/MockConsole.cs

+        /// Flushes any remaining buffered output to the ITestOutputHelper.
+        /// Call this at the end of a test to ensure all output is written.
+        /// </summary>
+        public void FlushOutput()


@copilot - please rename this so its clear it refers to the test logging. For example FlushTestLogging

Done in a518e4c. Renamed to FlushTestLogging to clarify it refers to test logging output.

…FlushTestLogging Co-authored-by: noahfalk <6243776+noahfalk@users.noreply.github.com>

Initial plan

32b8344

Copilot AI assigned Copilot and mdh1418 Jan 28, 2026

Copilot started work on behalf of mdh1418 January 28, 2026 02:49 View session

Copilot AI and others added 5 commits January 28, 2026 02:58

Add ITestOutputHelper support to improve console output visibility in…

c5b60ad

… CollectCommand tests Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Address code review feedback - improve output buffering and exception…

d8a661e

… handling Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Optimize output buffering and improve exception handling specificity

b36bac0

Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Final implementation complete - console output now visible in test fa…

a983c36

…ilures Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Remove accidentally committed nuget.exe

9cd25ad

Copilot AI changed the title ~~[WIP] Enhance console visibility for CollectCommand tests~~ Add ITestOutputHelper to MockConsole for visible console output in test failures Jan 28, 2026

Copilot AI requested a review from mdh1418 January 28, 2026 03:08

Copilot finished work on behalf of mdh1418 January 28, 2026 03:08

mdh1418 reviewed Jan 28, 2026

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src/tests/Common/MockConsole.cs Outdated Show resolved Hide resolved

src/tests/Common/MockConsole.cs Outdated Show resolved Hide resolved

Update src/tests/Common/MockConsole.cs

98b6a79

Copilot started work on behalf of mdh1418 January 28, 2026 19:14 View session

Address PR feedback: simplify comments, add FlushOutput, update Conso…

cf2edc3

…leExporterTests Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Copilot AI requested a review from mdh1418 January 28, 2026 19:23

Copilot finished work on behalf of mdh1418 January 28, 2026 19:23

mdh1418 marked this pull request as ready for review January 28, 2026 23:21

mdh1418 requested a review from a team as a code owner January 28, 2026 23:21

mdh1418 requested review from Copilot, hoyosjs and noahfalk January 28, 2026 23:21

Copilot started reviewing on behalf of mdh1418 January 28, 2026 23:21 View session

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Copilot started work on behalf of mdh1418 January 28, 2026 23:27 View session

Fix case-sensitive exception filter to use OrdinalIgnoreCase comparison

61ff689

Co-authored-by: mdh1418 <16830051+mdh1418@users.noreply.github.com>

Copilot finished work on behalf of mdh1418 January 28, 2026 23:34

noahfalk reviewed Jan 29, 2026

View reviewed changes

Copilot started work on behalf of noahfalk January 29, 2026 01:33 View session

Refactor: Extract BufferTestLogging helper and rename FlushOutput to …

a518e4c

…FlushTestLogging Co-authored-by: noahfalk <6243776+noahfalk@users.noreply.github.com>

Copilot AI requested a review from noahfalk January 29, 2026 01:41

Copilot finished work on behalf of noahfalk January 29, 2026 01:41

mdh1418 approved these changes Jan 29, 2026

View reviewed changes

	catch (InvalidOperationException ex) when (ex.Message.Contains("no currently active test"))
	catch (InvalidOperationException ex) when (ex.Message.Contains("no currently active test", StringComparison.OrdinalIgnoreCase))

Add ITestOutputHelper to MockConsole for visible console output in test failures #5700

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Add ITestOutputHelper to MockConsole for visible console output in test failures #5700

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Improve Console Output Visibility in CollectCommand Tests

Changes completed:

Key features:

Result:

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