Winforms: Debug.Assert failures don't appear in the CI

[hughbe]

E.g. in https://github.com/dotnet/winforms/pull/274 all the Debug CI says is: https://dnceng.visualstudio.com/public/_build/results?buildId=64113

2018-12-30T00:24:03.6894940Z ##[section]Starting: Windows Build / Publish
2018-12-30T00:24:03.6898330Z ==============================================================================
2018-12-30T00:24:03.6898453Z Task         : Command Line
2018-12-30T00:24:03.6898561Z Description  : Run a command line script using cmd.exe on Windows and bash on macOS and Linux.
2018-12-30T00:24:03.6899122Z Version      : 2.142.2
2018-12-30T00:24:03.6899213Z Author       : Microsoft Corporation
2018-12-30T00:24:03.6899310Z Help         : [More Information](https://go.microsoft.com/fwlink/?LinkID=613735)
2018-12-30T00:24:03.6899415Z ==============================================================================
2018-12-30T00:24:04.6567772Z Generating script.
2018-12-30T00:24:04.6682829Z Script contents:
2018-12-30T00:24:04.6688452Z eng\common\cibuild.cmd -configuration Debug -prepareMachine   
2018-12-30T00:24:04.7248531Z ##[command]"C:\Windows\system32\cmd.exe" /D /E:ON /V:OFF /S /C "CALL "F:\vsagent\_temp\8a2c7d10-e0e1-452c-b838-667c67b22baa.cmd""
2018-12-30T00:24:05.9551282Z dotnet-install: Downloading link: https://dotnetcli.azureedge.net/dotnet/Sdk/3.0.100-preview-009820/dotnet-sdk-3.0.100-preview-009820-win-x64.zip
2018-12-30T00:24:07.0731103Z dotnet-install: Extracting zip from https://dotnetcli.azureedge.net/dotnet/Sdk/3.0.100-preview-009820/dotnet-sdk-3.0.100-preview-009820-win-x64.zip
2018-12-30T00:24:36.1620892Z dotnet-install: Adding to current process PATH: "F:\vsagent\68\s\.dotnet\". Note: This change will not be visible if PowerShell was run as a child process.
2018-12-30T00:24:36.1648616Z dotnet-install: Installation finished
2018-12-30T00:24:36.9903158Z F:\vsagent\68\s\.dotnet\sdk\3.0.100-preview-009820\MSBuild.dll /noconsolelogger /nologo -maxcpucount /m -verbosity:m /v:minimal /bl:F:\vsagent\68\s\artifacts\log\Debug\ToolsetRestore.binlog /clp:Summary /nr:False /p:TreatWarningsAsErrors=true /p:__ToolsetLocationOutputFile=F:\vsagent\68\s\artifacts\toolset\1.0.0-beta.18621.6.txt /t:__WriteToolsetLocation /warnaserror F:\vsagent\68\s\artifacts\toolset\restore.proj
2018-12-30T00:24:39.2958371Z F:\vsagent\68\s\.dotnet\sdk\3.0.100-preview-009820\MSBuild.dll /nologo -maxcpucount /m -verbosity:m /v:minimal /bl:F:\vsagent\68\s\artifacts\log\Debug\Build.binlog /clp:Summary /nr:False /p:TreatWarningsAsErrors=true /p:Configuration=Debug /p:RepoRoot=F:\vsagent\68\s /p:Restore=True /p:DeployDeps=False /p:Build=True /p:Rebuild=False /p:Deploy=False /p:Test=True /p:Pack=True /p:IntegrationTest=False /p:PerformanceTest=False /p:Sign=True /p:Publish=True /p:Execute=False /p:ContinuousIntegrationBuild=True /warnaserror F:\vsagent\68\s\.packages\microsoft.dotnet.arcade.sdk\1.0.0-beta.18621.6\tools\Build.proj
2018-12-30T00:24:40.1225991Z   Restoring packages for F:\vsagent\68\s\.packages\microsoft.dotnet.arcade.sdk\1.0.0-beta.18621.6\tools\Tools.proj...
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2018-12-30T00:24:41.1104181Z   Restore completed in 974.54 ms for F:\vsagent\68\s\.packages\microsoft.dotnet.arcade.sdk\1.0.0-beta.18621.6\tools\Tools.proj.
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2018-12-30T00:24:43.7209738Z   Installing Microsoft.NETCore.DotNetAppHost 3.0.0-preview-27205-02.
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2018-12-30T00:24:44.2695456Z   Installing System.Drawing.Common 4.6.0-preview.18563.5.
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2018-12-30T00:24:51.8423361Z   Generating MSBuild file F:\vsagent\68\s\artifacts\obj\Microsoft.Private.Winforms\Microsoft.Private.Winforms.csproj.nuget.g.props.
2018-12-30T00:24:51.8481393Z   Generating MSBuild file F:\vsagent\68\s\artifacts\obj\System.Windows.Forms.Design.Editors.Ref\System.Windows.Forms.Design.Editors.Ref.csproj.nuget.g.props.
2018-12-30T00:24:51.8503909Z   Generating MSBuild file F:\vsagent\68\s\artifacts\obj\System.Drawing.Design.Facade\System.Drawing.Design.Facade.csproj.nuget.g.props.
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2018-12-30T00:26:01.7953336Z   Running tests: F:\vsagent\68\s\artifacts\bin\System.Windows.Forms.Design.Editors.Tests\Debug\netcoreapp3.0\System.Windows.Forms.Design.Editors.Tests.dll [netcoreapp3.0|x64]
2018-12-30T00:26:01.7961152Z   Running tests: F:\vsagent\68\s\artifacts\bin\System.Windows.Forms.Tests\Debug\netcoreapp3.0\System.Windows.Forms.Tests.dll [netcoreapp3.0|x64]
2018-12-30T00:26:02.7055374Z   Tests succeeded: F:\vsagent\68\s\artifacts\bin\System.Windows.Forms.Design.Editors.Tests\Debug\netcoreapp3.0\System.Windows.Forms.Design.Editors.Tests.dll [netcoreapp3.0|x64]
2018-12-30T00:26:02.9370821Z   Running tests: F:\vsagent\68\s\artifacts\bin\System.Windows.Forms.Design.Tests\Debug\netcoreapp3.0\System.Windows.Forms.Design.Tests.dll [netcoreapp3.0|x64]
2018-12-30T00:26:03.2815779Z XUnit : error : Tests failed: F:\vsagent\68\s\artifacts\log\Debug\System.Windows.Forms.Tests_netcoreapp3.0_x64.log [netcoreapp3.0|x64] [F:\vsagent\68\s\src\System.Windows.Forms\tests\UnitTests\System.Windows.Forms.Tests.csproj]
2018-12-30T00:26:04.5205385Z   Tests succeeded: F:\vsagent\68\s\artifacts\bin\System.Windows.Forms.Design.Tests\Debug\netcoreapp3.0\System.Windows.Forms.Design.Tests.dll [netcoreapp3.0|x64]
2018-12-30T00:26:04.9253866Z 
2018-12-30T00:26:04.9432462Z Build FAILED.
2018-12-30T00:26:04.9432790Z 
2018-12-30T00:26:04.9591796Z XUnit : error : Tests failed: F:\vsagent\68\s\artifacts\log\Debug\System.Windows.Forms.Tests_netcoreapp3.0_x64.log [netcoreapp3.0|x64] [F:\vsagent\68\s\src\System.Windows.Forms\tests\UnitTests\System.Windows.Forms.Tests.csproj]
2018-12-30T00:26:04.9592565Z     0 Warning(s)
2018-12-30T00:26:04.9592914Z     1 Error(s)
2018-12-30T00:26:04.9593171Z 
2018-12-30T00:26:04.9593579Z Time Elapsed 00:01:25.50
2018-12-30T00:26:05.0538074Z Build failed.
2018-12-30T00:26:05.0618424Z See log: F:\vsagent\68\s\artifacts\log\Debug\Build.binlog
2018-12-30T00:26:05.0681401Z Killing running build processes...
2018-12-30T00:26:05.2443878Z ##[error]Cmd.exe exited with code '1'.
2018-12-30T00:26:05.3264632Z ##[section]Finishing: Windows Build / Publish

[zsd4yr]

In this case, do you know which debug assert failed?

[hughbe]

Any of the debugs deleted in https://github.com/dotnet/winforms/commit/e267e523ed516d1c3fc2c331ec90fbd4d9cb3a19

[zsd4yr]

I agree this kind of thing should show up in the build as a debug assertion failure, not a test failure.

[AdamYoblick]

Debug asserts happen at runtime, not compile time. If the DEBUG tests are running, debug asserts will be hit I think.

---

From: Zachary Danz [e-mail]
Sent: Friday, January 4, 2019 3:10 PM
To: dotnet/winforms
Cc: Subscribed
Subject: Re: [dotnet/winforms] Debug.Assert failures don't appear in the CI (#277)

I agree this kind of thing should show up in the build as a debug assertion failure, not a test failure.

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[sharwell]

Debug assertions need a trace listener to work well in automated test scenarios. For example, see PerfView's use of ThrowingTraceListener. Note that the listener requires registration to work, which can be seen in https://github.com/Microsoft/perfview/commit/b846e8d0dc4dd3ca95061ad4adc3d309eaa88bb8. Adjustments may be required since that example runs on .NET Framework.

[AdamYoblick]

This is why I'm not a fan of Debug.Asserts in general. I get that they improve performance in release scenarios, but I would rather the test fail consistently if it's supposed to, in both debug and release.

[weltkante]

@AdamYoblick you are missing the point, this was a DEBUG run (see -configuration Debug switch in the log)

The point sharwell raises is that for CI you need some additional setup code to have Debug.Assert/Trace.Assert actually be treated as a test failure.

[AdamYoblick]

I understand what Sam is saying. :) This means we would need to change our test code based on the config being run, which I'm not a fan of. If my team disagrees, then I'm flexible of course.

In my opinion, all methods should use real error handling (i.e. throwing exceptions) instead of Debug.Asserts. This would eliminate the need for special test code for the debug config.

I understand the performance implications of this, which is why many people prefer to use Debug.Assert, especially in private methods (but we don't test private methods directly anyway)

[sharwell]

@AdamYoblick Debug.Assert can be helpful for things like internal invariants that should never be violated. For example, a private method could assert arguments are not null if both 1) all exposed callers validate arguments and 2) it's not immediately obvious from the code flow that the callers ensure the arguments are not null. In such a case, Debug.Assert is preferable to argument checking because the resulting IL is smaller/more efficient, without any actual change to behavior of the production code.

In some cases, Debug.Assert can be used in place of plain comments in code that make a statement regarding the state of one or more variables at a particular location in an algorithm. The assertions are not intended to change behavior, but rather document it. They offer an advantage over plain comments because they will call attention to themselves should the conditions ever change in the future.

In general, the assertions should not impact the test code.

[AdamYoblick]

First let me say that I know I'm in the minority with this opinion. Engineers tend to value performance over everything else, but I do not. :)

I get that Debug.Assert is better performance than throwing exceptions. My argument is that it's safer for every method (even privates) to just validate its own arguments with exceptions. This guarantees that the inputs are valid for any method, regardless of the call stack, regardless of the config.

I understand that means you are often validating the same argument multiple times, which is why people prefer Debug.Assert. But I prefer a safe (and properly unit testable) method over a little performance gain.

What if someone else (another dev) sees this private method and uses it, but doesn't realize they have to validate the args before passing them down? I would rather eliminate this possibility entirely and make my method bulletproof.

Again, I know this is not a popular opinion, but I've been burned too many times by methods not validating their own args. In my experience, the performance cost of a couple IF statements is worth the "stronger" code.

[karelz]

I agree with @AdamYoblick that runtime checks are in 99.9% cases better than Debug.Assert. Only 0.1% code may be so perf sensitive, that it matters and justifies use of Debug.Assert. Rather be sure (while a bit slower) than faster and sorry.
@stephentoub @danmosemsft does it match your guidence and experience in CoreFX?

[stephentoub]

I'm having trouble following the discussion. Can someone help me understand what the original problem is? By default a Debug.Assert will fail fast; is that not happening? Has it been overridden? Etc.

As for guidance, my view of Debug.Assert is basically the same as @sharwell: it's for validating that internal invariants aren't broken. In some cases, those internal invariants are for internal argument validation, and the lower you get in the stack, the more important it is not to keep paying for argument validation costs over and over and over, so while it might behoove a higher-level library to validate arguments with runtime checks and exceptions at every level of the stack, that's not the case for lower level libraries, like most of the ones in coreclr/corefx, so there it's common to see asserts used in internal/private helpers to sanity check that the inputs we're getting are what we expected.

[AdamYoblick]

@stephentoub In a nutshell, the suggestion was that Debug.Asserts should properly fail our unit tests. Sam mentioned that we could modify our test code to subscribe to a trace listener in order for debug asserts to properly fail unit tests when running against a debug config.

My comment was we should not have to do this. If a test case is supposed to fail, it should be using Assert.Throws and should be catching a real exception, not a debug assert.

[stephentoub]

Thanks for summarizing.

My comment was we should not have to do this.

If the tests in question are validating public surface area, then from my perspective no Debug.Assert should ever be triggerable. In such a case, there's a bad bug, either the assert itself is bad or the important invariant its validating isn't being held, and it fail fasts; this isn't something to be validating via Assert.Throws because you should never be able to cause such errors to happen via the public surface area.

However, I remember earlier discussions that were advocating for being able to use InternalsVisibleTo to unit test via internals rather than publics. If these asserts are triggering because of misuse at that level, I have no sympathy ;-)

[merriemcgaw]

I think the consensus is that we don't want Debug.Asserts to fail our CI builds.

[hughbe]

I would urge you to reconsider this issue. Debug assertions don’t even appear in the continuous integration, they simply fail. This issue isn’t about the merits or demerits or debug assertions but more that if a debug assert it hit in ci, it says “tests failed” but the tests succeeded percent is 100% and the stack trace is missing.

[hughbe]

By fail I mean the test run crashes

[AdamYoblick]

Ohh I see, I was under the impression that debug asserts didn’t fail the CI build. You’re saying they do in a weird way.

In my opinion, that means we should either get rid of all the debug asserts (since many are informational), or only run unit tests for the release config.

Or the third option what is what Sam suggested, which is add a trace listener for the debug asserts.

[karelz]

My understanding of what @stephentoub suggested above is:

• Debug asserts are useful
• When Debug assert fails, it should show up as test failure (i.e. "fail" CI build)

[AdamYoblick]

@merriemcgaw Reopening this because we misunderstood what was happening. This does currently affect the CI build.

I think I'm leaning towards @Shyam-Gupta 's suggestion of only running unit tests for the release config (since this is what customers consume anyway). This would prevent "informational" debug asserts from failing the CI build.

@dreddy-work @zsd4yr How do you feel about this?