Pester

💵 Please consider sponsoring nohwnd, fflaten or sponsoring Pester itself.

🌵 Documentation is available at https://pester.dev/docs/quick-start.

📦🔐 Pester is now signed. -SkipPublisherCheck should no longer be used to install from PowerShell Gallery on Windows 10.

📦🔐 Upgrading to 5.6.0 will show a "certificate changed" error, this is because a change in Root Certificate, and you have to specify -SkipPublisherCheck to update. More info below.

👩👨 We are looking for contributors! All issues labeled help wanted are up for grabs. They further split up into good first issue that are issues I hope are easy to solve. Bad first issue where I expect the implementation to be problematic or needs to be proposed and discussed beforehand. And the rest which is somewhere in the middle. If you decide to pick up an issue please comment in the issue thread so others don't waste their time working on the same issue as you. There is also contributor's guide that will hopefully help you.

Pester is the ubiquitous test and mock framework for PowerShell.

BeforeAll {
    # 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
    }
  }
}

Save this code example in a file named Get-Planet.Tests.ps1, and run Invoke-Pester Get-Planet.Tests.ps1, or just press F5 in VSCode.

Learn how to start quick with Pester in our docs.

The example above also has an annotated and production ready version here.

Installation

Pester runs on Windows, Linux, MacOS and anywhere else thanks to PowerShell. It is compatible with Windows PowerShell 5.1 and PowerShell 7.2 and newer.

Pester 3 comes pre-installed with Windows 10, but we recommend updating, by running this PowerShell command as administrator:

Install-Module -Name Pester -Force

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

Signing certificates

The certificate used for signing the code has changed in 5.6.0. Error is shown when updating the module. Below is the list of the certificates you can expect to be used when importing the module (going back to 2016)

Version|Authority|Thumbprint ---|---|--- 6.0.0-alpha4+|CN=DigiCert Trusted G4 Code Signing RSA4096 SHA384 2021 CA1, O="DigiCert, Inc.", C=US|147C2FD397677DC76DD198E83E7D9D234AA59D1A 5.6.0+|CN=DigiCert Trusted G4 Code Signing RSA4096 SHA384 2021 CA1, O="DigiCert, Inc.", C=US|2FCC9148EC2C9AB951C6F9654C0D2ED16AF27738 5.2.0 - 5.5.0|CN=DigiCert SHA2 Assured ID Code Signing CA, OU=www.digicert.com, O=DigiCert Inc, C=US|C7B0582906E5205B8399D92991694A614D0C0B22 4.10.0 - 5.1.1|CN=DigiCert SHA2 Assured ID Code Signing CA, OU=www.digicert.com, O=DigiCert Inc, C=US|7B9157664392D633EDA2C0248605C1C868EBDE43 4.4.3 - 4.9.0|CN=DigiCert SHA2 Assured ID Code Signing CA, OU=www.digicert.com, O=DigiCert Inc, C=US|CC1168BAFCDA3B1A5E532DA87E80A4DD69BCAEB1 3.0.3 - 4.4.2|No Certificate Found|No Certificate Found 3.4.0|CN=Microsoft Windows Production PCA 2011, O=Microsoft Corporation, L=Redmond, S=Washington, C=US|71F53A26BB1625E466727183409A30D03D7923DF

In all cases, except for version 3.4.0 that was signed directly by Microsoft, the Authenticode issuer for certificate is CN=Jakub Jareš, O=Jakub Jareš, L=Praha, C=CZ.

To successfully update the module when certificate changed, you need to provide -SkipPublisherCheck to the Install-Module command.

Features

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.

Assertions

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 assertions in our documentation.

Mocking

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 {}

        Remove-Cache

        Should -Invoke -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}
image:
  - Visual Studio 2017
  - Ubuntu
install:
  - ps: Install-Module Pester -Force -Scope CurrentUser
build: off
test_script:
  - ps: Invoke-Pester -EnableExit

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

Pester itself is built on AzureDevOps, and distributed mainly via PowerShell gallery.