How to support automatic variable $? for native mocks?

[krokofant]

Given this code:

Describe 'ExitCodes' {
  It 'Should catch exit codes with $? variable' {
    Mock git -Verifiable -MockWith {
      # This mock should call through to the real git command. Imagine it transforms some arguments.
      & (Get-Command -CommandType Application git) $args
    }
    & (Get-Command -CommandType Application git) --git-dir ~/missing/.git --work-tree ~/missing/.git/.. status
    $? | Should -BeFalse # Works
    $LASTEXITCODE | Should -Be 128

    git --git-dir ~/missing/.git --work-tree ~/missing/.git/.. status
    $? | Should -BeFalse # Breaks
    $LASTEXITCODE | Should -Be 128
  }
}

How can we have the second example, which uses the mock, to work as expected? So that the $? is false.

Pester 5.7.1 and PowerShell 7.4.6

---

Edit:
It does work if a cmdlet is used instead of the mock like this:

    Remove-Alias -Name git -ErrorAction Ignore
    function git {
      [CmdletBinding()]
      param (
        [Parameter(ValueFromRemainingArguments = $true)]
        [string[]] $args
      )
      & (Get-Command -CommandType Application git) $args
      if (!$? -OR $LASTEXITCODE -ne 0) {
        $PSCmdlet.WriteError([System.Management.Automation.ErrorRecord]::new(
            "Wrapped command failed with exit code $LASTEXITCODE",
            "WrappedCommandFailed",
            [System.Management.Automation.ErrorCategory]::InvalidOperation,
            $args
          ))
      }
    }

[nohwnd]

$? tells you if the last command succeeded, and a mock is a function, so it stays true as long as the function itself does not fail. This is not specific to mocking, a plain function does the same:

function f { & /bin/sh -c 'exit 128' }
f
$?             # True
$LASTEXITCODE  # 128

$LASTEXITCODE propagates fine, so assert on that.

To get $? false the mock would have to write an error, and that does not really work here. Write-Error in -MockWith does not flip it, and $PSCmdlet is $null inside the mock body so the WriteError from your edit is not available. throw does flip it, but it is terminating so probably not what you want.

Tested with Pester 6.1.0 on PowerShell 7.5.5.