test: Add Clear-PSBuildOutputFolder coverage

[MisterTriangle]

Summary

• I added focused Pester coverage for Clear-PSBuildOutputFolder.
• I verified that it removes an existing output folder and handles a missing folder without throwing.

Testing

• pwsh -NoProfile -File ./build.ps1 -Task Test -Bootstrap

Closes #94

[tablackburn]

Thanks for this — and welcome. This is exactly the kind of contribution the roadmap asked for:
#94 sits outside the v1.0.0 milestone, which only means it does not gate the release, and
#120 explicitly says contributions to these
test-backfill issues are welcome during the cycle. Closes #94 is right and should stay.

The tests themselves are good. They import the built module the way the rest of the suite does,
use $TestDrive so nothing needs cleaning up, and the two behaviors you picked — removes an
existing folder, tolerates a missing one — are the right first two.

I have updated the branch (it had fallen two commits behind main) and approved the workflow run,
so CI should report shortly. Nothing needed from you for either.

One test worth adding before this merges

The function's most important behavior is the one thing not covered yet:

[parameter(Mandatory)]
[ValidateScript({
        if ($_.Length -le 3) {
            throw ($LocalizedData.PathLongerThan3Chars -f $_)
        }
        $true
    })]
[string]$Path

with the comment just above it:

# Maybe a bit paranoid but this task nuked \ on my laptop. Good thing I was not running as admin.

That guard exists because this function once deleted a drive root. It is the highest-stakes line
in the module, it has no coverage anywhere in tests/ today, and a regression in it would be
genuinely destructive rather than merely wrong. Something like:

It 'refuses a path short enough to be a drive root' {
    { Clear-PSBuildOutputFolder -Path 'C:\' } | Should -Throw
}

Asserting on the message (PathLongerThan3Chars from PowerShellBuild/en-US/Messages.psd1) rather
than just that it throws would be even better, since it distinguishes the guard firing from some
unrelated failure.

Smaller: the removal test cannot see a missing -Recurse

$outputPath = Join-Path -Path $TestDrive -ChildPath 'Output'
New-Item -Path $outputPath -ItemType Directory -Force > $null

That directory is empty, and Remove-Item deletes an empty directory with or without -Recurse.
Putting a nested file inside it first would make the test exercise the recursive path that the
function actually relies on.

Neither of these is a criticism of what is here — they are the natural next two assertions, and I
would rather ask than add them myself, since it is your contribution. Happy to take it as is if you
would prefer; say the word and I will pick them up in a follow-up instead.

[MisterTriangle]

Thank you for the detailed review and the welcome. I added both suggestions:

• The removal test now creates Nested/marker.txt, so it exercises recursive removal.
• I added the drive-root guard test and asserted on the localized validation message. I mocked Test-Path so the test cannot reach the real filesystem if that validation ever regresses.

The focused test file passes 3/3, and the full ./build.ps1 -Task Test -Bootstrap run passes as well. Thank you for updating the branch and approving the workflow run.