Cmdlets in filePath that rely on parameter sets are not available in PowerShell 2

[alx9r]

PowerShell 2 isn't able to resolve parameter sets for some of the Cmdlets in filePath even though it should be able to. PowerShell 4 and later does not have this problem. The affected Cmdlets are simply not available when using PowerShell 2.

Here is the repro of the fundamental problem:

module.psm1

function f {
    [CmdletBinding()]
    param
    (
        [Parameter(ParameterSetName = 'A',
                   Mandatory        = $true)]
        $a,

        [Parameter(ParameterSetName = 'A',
                   Mandatory        = $true)]
        [Parameter(ParameterSetName = 'B',
                   Mandatory        = $true)]
        $ab

    )
    process
    {
        $PSCmdlet.ParameterSetName
    }
}

module.Tests.ps1

Import-Module module -Force

Describe f {
    It 'should use the "A" parameter set when both a and ab are provided.' {
        f -a 'a' -ab 'b' | Should be A
    }
    It 'should use the "B" parameter set when only ab is provided.' {
        f -ab 'b' | Should be B
    }
}

Results

The above tests pass in PowerShell 4. However, PowerShell 2 produces the following result: