Mocking Indirect Variables

I have been working with an API that returns some extra info in the response headers and so was looking forward to getting a lot of mileage out of the new -ResponseHeadersVariable parameter for Invoke-RestMethod, but as I was writing tests for my new functions I ran into an issue: How do you mock setting that kind of variable?

Turns out the answer was pretty simple, just use the old trusty Set-Variable function with the -Scope parameter. It took me a little bit of figuring out which scope to use and tried the value for the parent scope first (1), but it turns out that the script scope is all that’s needed.

function My-Function {
    $result = Invoke-RestMethod -Uri "https://api.somewhere.com/some/endpoint" -ResponseHeadersVariable responseHeaders
    $responseHeaders.SomeKey | Write-Output
}

Describe "My-Function" {
    It "Returns the value of SomeKey from the response headers" {
        $goodResponse = "Woot!"
        Mock -CommandName Invoke-RestMethod -MockWith { Set-Variable -Scope Script -Name responseHeaders -Value @{ SomeKey = $goodResponse }; return $true }
        My-Function | Should -Be $goodResponse
    }
}