Add test for github format of doctest report

[user202729]

As in the title.

The feature was added in #36938 for the purpose of showing GitHub annotations for test failures, but there wasn't a doctest for it. This adds the test.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview. (no change to documentation preview because private method.)

⌛ Dependencies

[github-actions]

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[kwankyu]

I am curious why the text "Failed example" shows twice (once in red and once in black), as seen:

? Is this intended?

[user202729]

It has always been like that, but looking at what the program prints out

 ::error title=Failed example:,file=.../sage/doctest/forker.py,line=12::Failed example:
    doctest_var = 42; doctest_var^2

a reasonable guess is the part being put after title= is the red part, and the rest is the code (annotation body).
Double check.

On the other hand in the downloaded log file only

[error]Failed example:
    doctest_var = 42; doctest_var^2

would show up. This actually slightly inconvenience me in that I can't just download the log and parse it for the file and line number.

(side note: There should probably be more tests for the %0A magic and stuff.)

[kwankyu]

It has always been like that, but looking at what the program prints out

 ::error title=Failed example:,file=.../sage/doctest/forker.py,line=12::Failed example:
    doctest_var = 42; doctest_var^2

a reasonable guess is the part being put after title= is the red part, and the rest is the code (annotation body).

Yes, it seems so. Thanks.

On the other hand in the downloaded log file only

[error]Failed example:
    doctest_var = 42; doctest_var^2

would show up. This actually slightly inconvenience me in that I can't just download the log and parse it for the file and line number.

I agree. Maybe something to be improved later, if possible.

[user202729]

this tests for whole-file timeout and failed example, although using unittest instead of command-line-based test.

the long time warnings are tested in #40413, so this should be good.

[dimpase]

LGTM