PowerShell: Pester Installation Guide

Introduction

In this article, I will introduce how to set up "Pester," a BDD-style testing framework.
By utilizing unit tests^[1] in PowerShell script development, you can develop high-quality scripts.
Below, I will explain the steps to install Pester.

About BDD and TDD

TDD (Test-Driven Development)

TDD (Test-Driven Development)^[2] is a development methodology that uses unit tests to improve code quality. By creating tests before writing the intended code, you can create code that is easy to test.

BDD (Behavior-Driven Development)

BDD (Behavior-Driven Development)^[3] is a methodology that performs unit testing with a focus on code behavior.

What is Pester?

Pester is a framework for writing unit tests for PowerShell scripts,
and by using the following three cmdlets, you can create a BDD-style test suite.

• Describe
• Context
• It

Main Cmdlets of Pester

Pester provides several cmdlets. Below, I introduce some of the commonly used ones.

Cmdlet	Description	Usage Example
New-Fixture	Creating a unit test scaffold	New-Fixture -Name sampleFunc1
Invoke-Pester	Executing unit tests	Invoke-Pester
Describe	Grouping unit tests	Describe <Script Name> { <Test Case> }
Context	Sub-grouping unit tests	Context <Context> { <Test Case> }
It	Defining test cases	It "<Test Description>" { <Test> }
Should	Assertion of test results	<Code to test> &#124 Should -BeTrue

An example of a unit test is as follows:

Describe `<Script Name>` {
  Context `<Context>` {
    It `<Test Name>` {
      `<Code to test>`| Should -Be `<Expected return value>`
    }
  }
}

For detailed descriptions of each cmdlet, please refer to the official website.

Basic Usage of Pester

The basic usage of Pester is as follows:

1. Create a test scaffold using New-Fixture.

2. Implement the test code using Describe, Context, and It.

3. Execute the tests using Invoke-Pester.

4. Implement the target code so that the created unit tests pass.

5. Repeat steps 2-4 until all features are implemented.

For detailed usage, please refer to the Pester official website.

Pester Installation Procedure

The following explains the procedure for installing the latest Pester v5.

1. Removing Pre-installed Pester

Remove the pre-installed old version of Pester using the following procedure (PowerShell must be run with administrator privileges).

1. Run the following command to unregister each Pester file:

$module = "C:\\Program Files\\WindowsPowerShell\\Modules\\Pester"
takeown /F $module /A /R
icacls $module /reset
icacls $module /grant "*S-1-5-32-544:F" /inheritance:d /T

2. Run the following command to delete each Pester file:

Remove-Item -Path $module -Recurse -Force -Confirm:$false

This completes the removal of the old Pester.

2. Installing the Latest Pester

Follow these steps to install Pester.

Use the following command with administrator or user privileges to install Pester from the PowerShell Gallery.

Install-Module Pester -Force -SkipPublisherCheck

3. Checking the Pester Version

After installation, check the version of Pester.
Use the following command to verify the version:

Get-Module -ListAvailable -Name Pester

If installed correctly, it will be displayed as follows:

    Directory: C:\\Program Files\\WindowsPowerShell\\Modules

ModuleType Version    PreRelease Name                                PSEdition ExportedCommands
---------- -------    ---------- ----                                --------- ----------------
Script     5.4.1                 Pester                              Desk      {Invoke-Pester, Describe, Context, It…}

Conclusion

I have explained how to install "Pester," a BDD-style testing framework for PowerShell script development.
By utilizing Pester, high-quality script development using unit tests becomes possible.
Let's make use of Pester in your PowerShell development.

References

Official

• Pester Official Website
• Microsoft PowerShell Official Documentation

Websites

• Pester - GitHub
• PowerShell Gallery

脚注

1. Unit test: A unit test using a testing framework.

2. TDD (Test-Driven Development): A development methodology that uses unit tests to improve code quality.

3. BDD (Behavior-Driven Development): A type of TDD focused on code behavior.