Pester: Getting Started with using Pester to test powershell

Pester is the framework for testing your powershell scripts, functions and modules. It is a BDD (behavior driven design) framework. Tests are written in, and executed by, powershell.

Install

Find-Module pester -Repository psgallery | Install-Module

Must run as an admin. May get this warning:

You are installing the modules from an untrusted repository. If you trust this repository, change its InstallationPolicy value by running the Set-PSRepository cmdlet. Are you sure you want to install the modules from 'https://www.powershellgallery.com/api/v2'?

...which is resolved with.

Set-PSRepository -Name 'PSGallery' -InstallationPolicy Trusted

That succeeded then retried installing pester.

I then received this error message:

> Find-Module pester -Repository psgallery | Install-Module
PackageManagement\Install-Package : A Microsoft-signed module named 'Pester' with version '3.4.0' that was previously installed conflicts with the new module
'Pester' from publisher 'CN=DigiCert Assured ID Root CA, OU=www.digicert.com, O=DigiCert Inc, C=US' with version '4.10.1'. Installing the new module may
result in system instability. If you still want to install or update, use -SkipPublisherCheck parameter.
At C:\Program Files\WindowsPowerShell\Modules\PowerShellGet\1.0.0.1\PSModule.psm1:1912 char:34
+ ...          $null = PackageManagement\Install-Package @PSBoundParameters
+                      ~~~~~ ~~~~~~~~~ ~~~~ ~~~~~ ~~~~~~~~ ~~~~~~~~~~ ~~~~~
		+ CategoryInfo          : InvalidOperation: (Microsoft.Power....InstallPackage:InstallPackage) [Install-Package], Exception
		+ FullyQualifiedErrorId : PublishersMismatch,Validate-ModuleAuthenticodeSignature,Microsoft.PowerShell.PackageManagement.Cmdlets.InstallPackage

So I tried:

Find-Module pester -Repository psgallery | Install-Module -SkipPublisherCheck

Get Help

Invoke-Pester -?
New-Fixture -?
New-PesterOption -?

Create new file

New-Fixture -Name Fire-LaserWeapon

Will create two pre-populated files:

...unless the file already exists in which case it skips that one and gives you a warning. (i.e. it won't overwrite your stuff)

Example of a test file:

Describe "Fire-LaserWeapon" {
	It "tries the impossible" {
		$true | Should Be $false
	}
	It "tries something easy" {
		$true | Should Be $true
	}
}

Running our tests

We can run those tests with:

Invoke-Pester -Script ./Fire-LaserWeapon.Tests.ps1

All Pester commands (today)

...found via:

which * | ? { $_.Source -eq "Pester" } | % {" - $($_.Name)"} | clipp

References