Pester and Powershell

Fun album, but daaang that kid looks annoying...

The transition from using manky old batch files through to powershell hasn’t been a smooth one for me.

It’s just too easy to whip up a *.bat file and get running, instead of using that fiddly “learnin” that us programmers are supposed to be good at.

---

Enter Pester

Yes - the ubiquitous testing framework for powershell. It’s been helpful so far…

Note to self - although pre-installed on Windows 10, update it with:

Install-Module -Name Pester -Force -SkipPublisherCheck

---

Testing ExecutionPolicy

This is a bit goofy, and helpful to explore the ExecutionPolicy stuff in powershell.

Make a file called … well, it says in the comments, but call it ExecutionPolicy.Tests.ps1
I tend to use a formula for these test files

#cd C:\Users\jfinnangelo\Desktop\pester
#Set-ExecutionPolicy Unrestricted

#Invoke-Pester -Script ./ExecutionPolicy.Tests.ps1
#Invoke-Pester -?
#get-help Invoke-Pester -examples

# Pester tests
Describe 'ExecutionPolicy' {

  Context "Set ExecutionPolicy" {
    It "Given valid Policy '<Policy>', it returns '<Expected>'" -TestCases @(
      @{ Policy = 'unrestricted'; Expected = 'Unrestricted' }
      @{ Policy = 'default'  ; Expected = 'Restricted' }
    ) {
      param ($Policy, $Expected)

      Set-ExecutionPolicy $Policy
      Get-ExecutionPolicy | Should Be $Expected
    }
  }
}

Set-ExecutionPolicy Default

Things to notice:

• Setting execution policy at the start, and resetting it at the end

---

How Modules work

Make a Module.Library.ps1 file:

Set-StrictMode  –version Latest

function Get-HelloValue($value)
{
    return "Hello " + $value
}

Things to notice:

• Did you notice the Set-StrictMode at the start? I like that.
• Syntax for a function
• Syntax for parameters
• string joining

Make a Module.Tests.ps1 file:

#cd C:\Users\jfinnangelo\Desktop\pester
#Set-ExecutionPolicy Unrestricted
#Set-ExecutionPolicy Default

#Invoke-Pester -Script ./Module.Tests.ps1
#Invoke-Pester -?
#get-help Invoke-Pester -examples

#https://stackoverflow.com/questions/8501225/how-to-call-a-function-in-another-powershell-script-when-executing-powershell-sc

function Get-HelloWorld
{
    return "Hello World"
}

# Pester tests
Describe 'Explore Powershell Modules' {

  BeforeAll {
    Set-StrictMode –version Latest
    . .\Module.Library.ps1
  }

  AfterAll {
  }

  Context "Check functions and referenced files" {

    It "Given the HelloWorld function, Then there is a result" {
      $result = Get-HelloWorld
      $result | Should Be "Hello World"
    }

    It "Given the HelloValue function in a separate file, Then there is a result" {
      $result = Get-HelloValue("Value")
      $result | Should Be "Hello Value"
    }
  }

  Context "Check StrictMode" {
    It "Given an undefined value, Then there is an exception" {
      { $result = $undefinedValue } | Should Throw "cannot be retrieved because it has not been set"
    }
  }
  
  Set-ExecutionPolicy Default
}

Things to notice:

• BeforeAll and AfterAll for tests
• Referencing the Module.Library.ps1 file with a .
• The Throw test

Here is the successful test run:

---

Cheers!