Pester is the ubiquitous test and mock framework for PowerShell.
JamesWTruher and nohwnd Take only the first instance of id or uname. (#1126)
Some *nix's have symbolic links such as /bin -> /usr/bin which cause Get-Command to retrieve multiple instances. This causes the module to not load on those systems.
Latest commit 163e3c4 Oct 19, 2018
Failed to load latest commit information.
.github Update GitHub templates (#1061) Sep 30, 2018
Dependencies Run all tests under Set-StrictMode set to Latest (#1041) May 9, 2018
Examples Use wildcards for tags (#1038) May 6, 2018
Functions Bump to 4.4.2 Oct 3, 2018
Snippets Corrected snippets to follow the new standard (#987) Feb 11, 2018
bin remove rouge link that appeared out of nowhere Feb 20, 2018
doc add sticker sources Sep 29, 2018
en-US Remove Than from GreaterOrEqual and LesOrEqual (#1046) May 21, 2018
lib Dev/gherkin-mocks (#936) Nov 12, 2017
vendor Bump to 4.1.1 Dec 9, 2017
.gitattributes Update Pester to work on PowerShell Core at Windows, Linux, macOS (#925) Nov 11, 2017
.gitignore Remove PowerCuke May 19, 2016
.travis.yml Add tests to verify completeness of a comment based help (#997) Feb 20, 2018 Bump to 4.4.2 Oct 3, 2018
LICENSE Added Apache version 2.0 license Aug 23, 2011
Pester.Tests.ps1 Allow assertions with multiple aliases (#1122) Oct 16, 2018
Pester.nuspec fix deploy Feb 20, 2018
Pester.psd1 Bump to 4.4.2 Oct 3, 2018
Pester.psm1 Take only the first instance of id or uname. (#1126) Oct 19, 2018 Document integration with AppVeyor Ubuntu build (#1051) Jul 25, 2018
VERIFICATION.txt Create VERIFICATION.txt (#957) Dec 17, 2017
buildNugetPackage.ps1 Fix whitespace Nov 30, 2017
buildPSGalleryPackage.ps1 fix deploy Feb 20, 2018
chocolateyInstall.ps1 The test 'Style Rules' corrected to include also files from the modul… Mar 22, 2017
getNugetExe.ps1 Bump to 4.1.1 Dec 9, 2017
nunit_schema_2.5.xsd NUnit OutputXML updated Jun 29, 2014
publishPSGalleryPackage.ps1 Build packages in PowerShell scripts Nov 30, 2017
report.dtd Add support for JaCoCo XML code coverage reports. (#782) Jul 12, 2017


Pester is the ubiquitous test and mock framework for PowerShell.

# your function
function Get-Planet ([string]$Name='*')
  $planets = @(
    @{ Name = 'Mercury' }
    @{ Name = 'Venus'   }
    @{ Name = 'Earth'   }
    @{ Name = 'Mars'    }
    @{ Name = 'Jupiter' }
    @{ Name = 'Saturn'  }
    @{ Name = 'Uranus'  }
    @{ Name = 'Neptune' }
  ) | foreach { [PSCustomObject]$_ }

  $planets | where { $_.Name -like $Name }

# Pester tests
Describe 'Get-Planet' {
  It "Given no parameters, it lists all 8 planets" {
    $allPlanets = Get-Planet
    $allPlanets.Count | Should -Be 8

  Context "Filtering by Name" {
    It "Given valid -Name '<Filter>', it returns '<Expected>'" -TestCases @(
      @{ Filter = 'Earth'; Expected = 'Earth' }
      @{ Filter = 'ne*'  ; Expected = 'Neptune' }
      @{ Filter = 'ur*'  ; Expected = 'Uranus' }
      @{ Filter = 'm*'   ; Expected = 'Mercury', 'Mars' }
    ) {
      param ($Filter, $Expected)

      $planets = Get-Planet -Name $Filter
      $planets.Name | Should -Be $Expected

    It "Given invalid parameter -Name 'Alpha Centauri', it returns `$null" {
      $planets = Get-Planet -Name 'Alpha Centauri'
      $planets | Should -Be $null

This code example lies a tiny bit, find it annotated and production ready here.

Learn more about the usage and syntax on our wiki.


Pester is compatible with Windows PowerShell 2.x - 5.x on Windows 10, 8, 7, Vista and even 2003. Since version 4.0.9 Pester is compatible also with PowerShell Core 6.x on Windows, Linux, macOS but with some limitations.

Pester comes pre-installed with Windows 10, but we recommend updating, by running this PowerShell command as administrator:

Install-Module -Name Pester -Force -SkipPublisherCheck

Not running Windows 10 or facing problems? See the full installation and update guide.


Test runner

Pester runs your tests and prints a nicely formatted output to the screen.

test run output

Command line output is not the only output option, Pester also integrates with Visual Studio Code, Visual Studio, and any tool that can consume nUnit XML output.


Pester comes with a suite of assertions that cover a lot of common use cases. Pester assertions range from very versatile, like Should -Be, to specialized like Should -Exists. Here is how you ensure that a file exists:

Describe 'Notepad' {
    It 'Exists in Windows folder' {
        'C:\Windows\notepad.exe' | Should -Exist

Learn more about assertion on our wiki.


Pester has mocking built-in. Using mocks you can easily replace functions with empty implementation to avoid changing the real environment.

function Remove-Cache {
    Remove-Item "$env:TEMP\cache.txt"

Describe 'Remove-Cache' {
    It 'Removes cached results from temp\cache.text' {
        Mock -CommandName Remove-Item -MockWith {}


        Assert-MockCalled -CommandName Remove-Item -Times 1 -Exactly

Learn more about Mocking here.

Code coverage

Pester can measure how much of your code is covered by tests and export it to JaCoCo format that is easily understood by build servers.

JaCoCo code coverage report

Learn more about code coverage here.

Build server integration

Pester integrates nicely with TFS, AppVeyor, TeamCity, Jenkins and other CI servers.

Testing your scripts, and all pull requests on AppVeyor is extremely simple. Just commit this appveyor.yml file to your repository, and select your repository on the AppVeyor website:

version: 1.0.{build}
- Visual Studio 2017
- Ubuntu
- ps: Install-Module Pester -Force -SkipPublisherCheck -Scope CurrentUser
build: off
- ps: Invoke-Pester -EnableExit

See it in action here! In case you do not need to test your scripts against PowerShell Core, just simply remove entire line mentioning Ubuntu.

Pester itself is build on the community build server and Travis CI, and distributed mainly via PowerShell gallery.

windows build linux/macos build latest version downloads

Further reading

Do you like what you see? Learn how to use Pester with our wiki guide, and continue with some of the other resources.

Got questions?

Got questions or you just want to get in touch? Use our issues page or one of these channels:

Pester Twitter Pester on StackOverflow Testing channel on Powershell Slack Pester Gitter Pester on