Differences in required test baseline files between stage 1 and stage 2 builds

[mthalman]

The release of 6.0.116 exposed an issue in the tests that make use of baseline files. That release caused a need to update the MissingXmlDoc.txt baseline file to include a new entry. But updating that file then caused the corresponding VerifyTargetingPacksHaveDoc test to fail in the stage 2 build (internal link) because the XML file was not missing in that build. So there's a difference in the output of the stage 1 and stage 2 build such that a single baseline file cannot describe the expected output of both scenarios.

This is expected to occur for other baseline files such as SDK diff and poison leaks. We should have a general solution that can apply to all these baseline file types.

One potential solution for this is to have two baseline files: one for the stage 1 build and the other for the stage 2 build. The pipeline would indicate which one to use via an environment variable. The baseline for the stage 2 build could be optionally such that if it does not exist, the test falls back to the stage 1 baseline.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[MichaelSimons]

@mthalman - Is this issue still relevant?

1. XmlDocTests were removed from all supported branches (XmlDocTests are redundant with SdkContentTests #3031)
2. PoisonTests baseline is intended to be empty. Only reason for entries is temporary and we should not be releasing with leaks
3. SdkContentTests now only run against stage 1 legs

#2 and #3 can affect servicing branches but IIRC they haven't been problematic. It was really #1 that prompted this issue.

[mthalman]

The only known occurrence of this issue currently is SDK content diff in servicing. It's fine to ignore that for servicing.