The PowerShell module Pester can be used to build unit tests for scripts and functions. Unit tests target the smallest possible unit of code, which, in PowerShell, is likely to be a function or a method in a PowerShell class.

Pester tests are saved in a file named ending with .tests.ps1 and executed using the command Invoke-Pester.Invoke-Pester finds files named *.tests.ps1 under a given path and executes all tests in each.

Describe and Should statements may also be entered in the console when exploring syntax, but this is not the normal method of defining and running tests.

While Pester is included with Windows 10, it is not the latest version. The latest version may be installed from the PSGallery:

Install-Module Pester -Force