Add ITestOutputHelper to MockConsole for visible console output in test failures

[Copilot]

Improve Console Output Visibility in CollectCommand Tests

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

Changes completed:

• Modified MockConsole to accept optional ITestOutputHelper parameter
• Updated MockConsole.Write methods to multiplex output to ITestOutputHelper when provided
• Injected ITestOutputHelper into CollectCommandFunctionalTests
• Injected ITestOutputHelper into CollectLinuxCommandFunctionalTests
• Injected ITestOutputHelper into ConsoleExporterTests
• Updated all test methods to pass ITestOutputHelper to MockConsole
• Optimized implementation to avoid unnecessary string allocations
• Made exception handling more specific with exception message check
• Added FlushTestLogging method to ensure buffered output is written
• Simplified comments per code review feedback
• Fixed case-sensitive exception filter to use OrdinalIgnoreCase comparison
• Refactored test logging logic into BufferTestLogging helper method
• Renamed FlushOutput to FlushTestLogging for clarity
• Verified backward compatibility with existing tests
• All tests pass successfully

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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[mdh1418]

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

[Copilot]

@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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[mdh1418]

@copilot apply changes based on the comments in this thread

[mdh1418]

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>

[Copilot]

@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.