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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.

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    You're not building your scripts in a way that is able to be tested. Furthermore, your functions shouldn't call each other in their definitions.. Commented Jan 30, 2018 at 4:09
  • 3
    Before dot-sourcing your script, try set-alias main out-null. It should suppress the call to main. After dot-sourcing, you may remove this alias. Commented Jan 30, 2018 at 4:11

3 Answers 3

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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 (e.g 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.

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Thanks. I have some shared code in a psm1 and I guess I will be separating business logic and front end in the future to make it easier to test code.
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If you, for some reason

  • want to keep all functionality in a single script (as opposed to in a module or split into multiple files)
  • need the functionality to be executed when the script is dot sourced
  • want to test the script's functionality using Pester
  • don't mind adding some testability enhancing logic to the script

one approach is to add logic that skips auto-executing the script's functionality when a switch parameter is supplied.

I use something like that to keep my Azure Automation runbooks simple (simplicity is debatable; here "simple" translates to "keeping all functionality in a single script file") and testable:

SingleScript.Tests.ps1

BeforeAll { . $PSScriptRoot/SingleScript.ps1 -InTestContext } Describe 'SingleScript' { Context 'Invoke-Functionality' { It 'invokes script functionality' { $result = Invoke-Functionality $result | Should -Be 'Something useful' } } }

In the test file above, within the BeforeAll block, auto-execution when dot sourcing is skipped with the switch parameter InTestContext.

SingleScript.ps1

param( [switch] $InTestContext ) function Invoke-Functionality { 'Something useful' } if (-not $InTestContext) { Invoke-Functionality }

In the script file above, you can see the logic that allows skipping auto-execution.

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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 }
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2 Comments

This seems very useful but how are you importing this into the Pester file to avoid the entire script running?
I was able to get this working by using $MyInvocation.InvocationName -match ".+.ps1" so that the Main function will only trigger when started by calling a script, rather than importing the script from a different script (or Pester file).

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