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Version: v6 (preview) 🚧

Installation and Update

Compatibility​

Pester is a cross-platform module that runs on Windows, Linux, MacOS and anywhere else running a supported version of PowerShell. Pester currently requires and is tested with:

  • Windows PowerShell 5.1
  • PowerShell 7.2 and above

You can install Pester using the built-in Install-Module command. The examples below will install Pester in your default installation scope depending on your PowerShell-version. You can control this using the -Scope <AllUsers/CurrentUser> parameter.

Linux & MacOS​

From a PowerShell session run:

Install-Module -Name Pester

To update:

Update-Module -Name Pester

Windows​

Windows 10 / Windows Server 2016 and later ships with Pester version 3.4.0. This built-in version cannot be updated using the simple Update-Module cmdlet. Instead you need to perform a side-by-side installation to get started with the latest version of Pester.

The built-in version is signed by Microsoft while newer versions are community-maintained and signed with a different certificate, causing Install-Module to sometimes throw a error requiring us to accept the new publisher certificate.

Run the command below to install the latest version:

# -Force to install side-by-side
# -SkipPublisherCheck to accept the newer certificate

Install-Module -Name Pester -Force -SkipPublisherCheck

For any subsequent updates it is enough to run:

Update-Module -Name Pester
Removing the built-in version

If you'd like to remove the built-in version of Pester, you can do so using the following code as administrator:

$module = "C:\Program Files\WindowsPowerShell\Modules\Pester"
& takeown.exe /F $module /A /R
& icacls.exe $module /reset
& icacls.exe $module /grant "*S-1-5-32-544:F" /inheritance:d /T
Remove-Item -Path $module -Recurse -Force -Confirm:$false

# Install latest Pester
Install-Module -Name Pester

Common errors​

If you receive the following warning when trying to install the module, you may need to explicitly enable TLS 1.2.

WARNING: Unable to resolve package source 'https://www.powershellgallery.com/api/v2'.

# Enable TLS 1.2 for the current PowerShell instance using the line below and try again
[System.Net.ServicePointManager]::SecurityProtocol = [System.Net.ServicePointManager]::SecurityProtocol -bor [System.Net.SecurityProtocolType]::Tls12

Installing manually​

You don't have to use a package manager to install Pester. Another option is to download and installing it manually which can be useful in e.g. offline environments.

  1. Download the module on a machine with internet using either:
    • Save-Module -Name Pester -Path C:\Temp. It will save it in a versioned folder, ex C:\Temp\Pester\5.5.0
    • Or download the NuGet package from PowerShell Gallery and extract it, see Manual Package Download
  2. Copy the Pester-folder (ex. C:\Temp\Pester) to your destination computer and place it in one of your module directories defined by $env:PSModulePath. On a Windows-system the default locations include:
    • Current user: $HOME\Documents\WindowsPowerShell\Modules
    • All users: $env:ProgramFiles\WindowsPowerShell\Modules
  3. Start PowerShell and start testing.
note

Step 2 is an optional step to enable simple import by name and module auto-loading. You could also import Pester using an absolute path like Import-Module C:\Temp\Pester\5.5.0.

Alternative package sources​

PSGallery is the easiest way to get Pester installed to your computer, but there are alternatives. On a build server you might prefer using Chocolatey, or if you're adding Pester to your .NET project that already uses NuGet you might prefer that.

These options may not support pre-release versions and it may need to be initialized on first use.

Chocolatey​

Chocolatey (or choco) is a commonly used package manager for Windows. You can install Pester using:

choco install Pester

Or to update:

choco upgrade Pester

You may also pass the --prerelease option to install or update to a prerelease version of Pester.

Nuget​

Nuget is the package manager for .NET projects. Getting Pester from Nuget is useful when you are integrating PowerShell code with your .NET project, and want to have that code tested.

To install use Package Manager of Visual Studio, or Package Manager Console in Visual Studio. Once you need this we are pretty sure you know what you are doing. 🙂