Test fixture for https://stackoverflow.com/q/46428736/1404637

test.ps1

New-Module m {
    function SomeScriptblockInvoker {
        param
        (
            [Parameter(Position = 1)]
            [scriptblock]
            $Scriptblock,

            [Parameter(ValueFromPipeline)]
            $InputObject
        )
        process
        {
            $modifiedLocal = 'variable name collision'
            $local = 'variable name collision'
            $InputObject | . $Scriptblock
        }
    }
} |
    Import-Module

Describe command {
    $sb = {
        $modifiedLocal = 'modified local value'
        [pscustomobject] @{
            Local = $local
            DollarBar = $_
        }
    }
    foreach ( $commandName in 'ForEach-Object','SomeScriptblockInvoker' )
    {
        Context $commandName {
            $modifiedLocal = 'original local value'
            $local = 'local'
            $r = 'input object' | & $commandName $sb
            It 'Local is accessible' {
                $r.Local | Should be 'local'
            }
            It 'DollarBar is input object' {
                $r.DollarBar | Should be 'input object'
            }
            It 'modifies local variable' {
                $modifiedLocal | Should be 'modified local value'
            }
        }
    }
}