Deduplicate path separator duplicates

[philderbeast]

Fixes #10645, a small Windows gotcha missed with #10546.

I really had to get into the weeds with this one. The assertOutputContains function was modifying the output (a test actual value) before comparision with the unmodified actual value. This change was not visible. I've added an assertOn function (that assertOutputContains calls) that takes a NeedleHaystack configuration for how the search, expectation and display are made. I had wanted to add a pilcrow ¶ for line endings but the terminal output is restricted to ASCII so I've marked line beginnings with ^ and line endings with $. The needle (the expected output fragment) is shown annotated this way as can the haystack (the output). The haystack is not shown annotated with line delimiters but can be.

The concatOutput function, I've renamed to lineBreaksToSpaces. There's more detail on the cabal-testsuite changes in the changelog entry. One benefit of using an .md extension for changelog.d/pr-10646.md is that typos are caught by CI.

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• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
  • Is the change significant? If so, remember to add significance: significant in the changelog file.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have been added. Yes, a doctest.

[geekosaur]

I'm confused: is the .md file a GitHub artifact, or did you really add two changelog.d entries?

[philderbeast]

I'm confused: is the .md file a GitHub artifact, or did you really add two changelog.d entries?

Thanks for catching that mistake of mine @geekosaur. I let the .md slip in. I rename locally to check the markdown preview. I've deleted that extra file now.

Can we use a .md extension for changelog.d entries?

[geekosaur]

changelog-d doesn't care; the only special name is config, where its own configuration is stored, and you can't use subdirectories. It might even be better to use the extension, since that way GitHub will also render it (although it will probably be confused by the YAML frontmatter).

[philderbeast]

Reverting to draft while I settle some Windows versus POSIX file path issues.