Pester: How do I keep my script from running?

Question

I am testing a PowerShell script. I'd like to test individual functions without executing the entire script. I am not sure if this is the intended use case or supported, and I am not finding a good answer searching online

sut.ps1:

Param(
    [Parameter(Mandatory = $true,
        Position = 0)]
    [ValidateNotNullOrEmpty()]
    [string] $Message
)

function fut([string] $argument) {
    Write-Host $argument
}

function Main() {
    fut($Message)
}

Main

sut.tests.ps1:

$here = Split-Path -Parent $MyInvocation.MyCommand.Path
$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
. "$here\$sut" "Message"

Describe "fut" {
    It "does something useful" {
        fut 'beer'
    }
}

Output

Message
Describing fut
beer
 [+] does something useful 385ms
Tests completed in 385ms

Now I can mock away 'beer', because it runs in the describe block. But I cannot mock away 'message', because the script starts to execute when I dot-source it.

In my case, 'message' is an operation I do not want to execute.

I am on Windows 10 15063.

Answer 1

Per the comments, the issue is that your script is self-executing, so it's not possible to load it for Pester via dot-sourcing without also executing the functions.

The workaround suggested by Roman to temporarily use Set-Alias to set main to Out-Null would work. Another suggestion would be to separate your functions to a separate file (eg named functions.ps1 ) and then in your original script you can use dot sourcing to include it, but in your test script just dot source the functions.ps1 file.

Answer 2

This will only run the main function if it is not called ny Dot Source, as a pester script would. I am using this instead of splitting functions to another file where it is not needed. Then pester runs without invoking the Main function.

if (-not ($MyInvocation.InvocationName -eq "."))
{
    Main
}