---
title: "PowerShell Pester 101: A Practical Guide for Beginners"
description: "Learn how to validate your PowerShell scripts with Pester testing. This hands-on guide shows you how to write tests that ensure your code works as intended."
canonical: "https://adamtheautomator.com/powershell-pester-testing-guide/"
---

# PowerShell Pester 101: A Practical Guide for Beginners

> Learn how to validate your PowerShell scripts with Pester testing. This hands-on guide shows you how to write tests that ensure your code works as intended.

Source: https://adamtheautomator.com/powershell-pester-testing-guide/

---

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# PowerShell Pester 101: A Practical Guide for Beginners

[![](https://secure.gravatar.com/avatar/d0b9d42e21e5622713f8b693aa5c0f9244d5f7dd200ed29b8398f52dee5de337?s=192&d=mm&r=g)Adam Bertram](https://adamtheautomator.com/author/adam-bertram/)9 January 20252 min. read

Categories: [IT Ops](/category/it-ops/)

Tags:[Pester](/tag/pester/)[PowerShell](/tag/powershell/)

Table of Contents

*   [Installing and Configuring Pester](#installing-and-configuring-pester)
*   [Creating a Pester Test File](#creating-a-pester-test-file)
*   [Adding and Running a Test](#adding-and-running-a-test)
*   [Conclusion](#conclusion)

When you run a script, how can you be sure it did exactly what you intended? Maybe it removed a file or stopped a service. But did it do so flawlessly across every environment, user session, or machine it touched? If your script impacts dozens—testing with Pester is your best bet.

Pester, the powerful PowerShell module, helps you write automated tests using a domain-specific language (DSL). In this tutorial, you’ll learn to eliminate the guesswork and create a rock-solid process to validate your scripts.

Buckle up and let Pester boost your scripting confidence!

## Installing and Configuring Pester

Pester ensures your script’s actions match your expectations in any environment. Testing with Pester is an essential skill for managing infrastructure with PowerShell.

But first, we need to install Pester to build some tests around a script that provisions a server to see how Pester tests work.

You can download the `Pester` module from the PowerShell Gallery:

```powershell
Install-Module Pester
```

If you encounter a warning, it might be because Windows 10 (and later) clients have an older version of Pester installed by default. For example, version 3.4.0 is often pre-installed.

Ensure you remove the old version to avoid conflicts:

```powershell
$module = "C:\Program Files\WindowsPowerShell\Modules\Pester\3.4.0"
takeown /F $module /A /R
icacls $module /reset
icacls $module /grant "*S-1-5-32-544:F" /inheritance:d /T
Remove-Item -Path $module -Recurse -Force -Confirm:$false
```

This script takes ownership of the Pester 3.4.0 folder, updates permissions, and removes it.

Install Pester’s latest version by appending the `-Force` parameter:

```powershell
Install-Module Pester -Force
```

You might see another warning regarding the new version’s signature. Microsoft signed the pre-installed version, whereas Pester’s maintainer, Jakub, signed the latest version.

Verify the installed version with the following command:

```powershell
Get-Module -Name Pester -ListAvailable
```

## Creating a Pester Test File

Now that Pester is installed let’s create some tests. For demonstration purposes, assume a script is tasked with installing the IIS Windows feature.

Create a PowerShell script named _ServerProvisioning.Tests.ps1_ in your desired directory; let’s say it’s in your ~\\Documents folder.

Next, execute Pester tests with the `Invoke-Pester` cmdlet:

```
cd ~\Documents
Invoke-Pester
```

Running this command without any tests available results in no tests being executed.

Let’s add some tests using Pester’s hierarchical block structure, where:

*   **`describe` r**epresents a category of tests, such as a script’s major functionality.
*   **`context`** optionally organizes tests into subcategories.
*   **`it`** defines individual tests.

```
describe 'IIS' {
    context 'Windows features' {
        it 'installs the Web-Server Windows feature' {

        }
    }
}

describe 'RegistryTweaks' {

}

describe 'SoftwareInstalls' {

}
```

## Adding and Running a Test

Imagine a script that provisions a server but misses a crucial step, like enabling a required feature. If left unchecked, this oversight can cause cascading issues in production.

Suppose the server provisioning script has run, and the task is to confirm that the `Web-Server` feature is installed. If so, perform a manual check.

Run the following command to manually check if the `Web-Server` feature (IIS) is installed on the remote server.

```powershell
Invoke-Command -ComputerName SRV1 -ScriptBlock { (Get-WindowsFeature -ComputerName SRV1 -Name Web-Server).Installed }
```

This command returns `True` if the feature is installed and `False` otherwise.

Now, add the following to the `it` block to automate this test. The `should` operator with the `-BeTrue` condition asserts that the feature is installed.

```
describe 'IIS' {
    context 'Windows features' {
        it 'installs the Web-Server Windows feature' {
            Invoke-Command -ComputerName SRV1 -ScriptBlock { (Get-WindowsFeature -ComputerName SRV1 -Name Web-Server).Installed } | should -BeTrue
        }
    }
}
```

Finally, rerun the test:

```
cd ~\documents
Invoke-Pester
```

As expected, the test will fail if the feature isn’t installed.

* * *

**__VS Code has some great Pester integration, too. Instead of running `Invoke-Pester`, you can click the `Run Tests` item on individual tests directly in VS Code. This action invokes specific tests.__**

* * *

## Conclusion

In this tutorial, you learned how to use Pester to automate testing for your PowerShell scripts. You’ve covered the foundational steps to validate your scripts effectively. These steps include installing and configuring Pester, creating a test file, and writing your first automated test.

Build on this foundation by exploring how Pester can handle more advanced scenarios, such as testing APIs, mocking commands, or running pre- and post-deployment validations.

As you integrate Pester into your workflow, you’ll improve your scripts and gain trust in their reliability—confidently scale your automation efforts!

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