Dot sourcing

dot.ps1

Import-Module Pester -MaximumVersion 4.9.9

# use the fact that closures are dynamic modules with 
# their own session state, and that scriptblocks are bound
# to the session state that created them, that makes 
# the call to `dot` transparent, because the scope
# that the function creates is in a different sessionstate
# and so the `$ScriptBlock` still dot-sources directly into
# the calling session state, just like with the naked `.`
$function:dot = { 
    param($ScriptBlock)
    . $ScriptBlock
}.GetNewClosure()

Describe "a" { 
    It "dot sources" {
        $a = 1
        # ensure that we are running the same scope
        # by writing into the `$a` variable
        dot { $a = 20 }
        $a | Should -be 20
    }

    It "can be mocked" { 
        Mock dot { Write-Host "I am mock" -ForegroundColor Cyan }
        $a = 1
        dot { $a = 20 }
        $a | Should -Be 1
    }
}