How to test for ShouldProcess and Confirm?

[thomykay]

Any idea how to test for ShouldProcess and Confirm support using PSate? The whatif output can be checked with Should, but how to test Confirm?

[jonwagner]

That's a tough one.

I assume you have a function like this:

function Test {
    [CmdletBinding(SupportsShouldProcess=$true, ConfirmImpact="High")]
    param()
    process {
        if ($PSCmdlet.ShouldProcess("test")) {
            "Doing it"
        }
    }
}

Test

If you're writing a dangerous action, you probably want to write tests like:

• If confirm is true and the user hits cancel, the action is not performed
• If confirm is true and the user hits ok, the action is performed

In this case, you want to control the output of $PSCmdlet.ShouldProcess. I think the easiest way to do this is to create another function called CheckShouldProcess that just calls $PSCmdlet.ShouldProcess. Then you can use PSMock to mock the function and control the outputs. Something like this:

Enable-Mock | iex

function CheckShouldProcess {
    param (
        $target
    ) 
    $PSCmdlet.ShouldProcess($target)
}

function Test2 {
    [CmdletBinding(SupportsShouldProcess=$true, ConfirmImpact="High")]
    param()
    process {
        if (CheckShouldProcess("test")) {
            "Doing it"
        }
    }
}

Mock CheckShouldProcess { $false }
Test2  # no prompt and does not perform the action
Mock CheckShouldProcess { $true }
Test2  # no prompt and performs the action
Clear-Mocks
Test2  # prompts for a response

It might also be possible to replace $PSCmdlet with a new PSObject where you control the ShouldProcess method, but since $PSCmdlet is an automatic variable, it probably wouldn't be too easy.

[thomykay]

Indeed, mocking (the whole) $PSCmdlet variable seems to be a bit hard and might also interfere with other code using it.

Thanks for your thoughts on this. Very helpful.

In general: I've used the PSate, PShould combination for some days now and I really like it. Eventually it's fun to write tests for PowerShell modules.

[jonwagner]

Also, if you have more advanced testing scenarios, you can use parameters in the Mock:

Mock CheckShouldProcess { param ($target) { if ($target == "foo") return $true; else return $false;  } }

Enjoy.