Leaking parent scope fools my tests

options.ps1

function A { 
    [CmdletBinding()]
    param() 

    if ($null -eq $Option) { throw }
}

Describe "A" {
    it "works" {
        $option = "abc"
        # $option leaks into the function A
        # that forgot to define it's parameters
        # and the test passes
        A
    }
}


function B { 
    [CmdletBinding()]
    param() 

    if ($null -eq $local:Option) { throw }
}

Describe "B" {
    it "works" {
        $option = "abc"
        # $option leaks into the function B
        # that forgot to define it's parameters
        # but we only look at local variables
        # so the test fails
        B
    }
}

A more real-life example that caused me a lot of problems:

function A { 
    [CmdletBinding()]
    param($Option) 

    C
}

function C { 
    [CmdletBinding()]
    param() 

    if ($null -eq $Option) { throw }
}

Describe "A" {
    it "works" {
        A -Option "abc"
    }
}

$tests = {
    function A { 
        [CmdletBinding()]
        param($Option) 

        C
    }

    function C { 
        [CmdletBinding()]
        param() 

        $caseSensitive = $null -eq $Option -or $Option.CaseSensitive
        # do some more stuff
    }

    Describe "A" {
        it "works" {
            A -Option @{ CaseSensitive = $true }
        }
    }



    Describe "C" {
        it "works" {
            C
        }
    }
}


Set-StrictMode -Off 
&$tests
Set-StrictMode -Version Latest
&$tests