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Prerequisites

Before building anything, let's make sure the tools are in place. This page is short, but the version check at the end matters more than it looks — a surprising number of confusing Pester problems turn out to be "you are running an older version than you think".

PowerShell​

Pester v6 runs on:

  • Windows PowerShell 5.1, or
  • PowerShell 7.4 or newer

Check what you have:

$PSVersionTable.PSVersion

If you are on PowerShell 7 but older than 7.4, install a current release from the PowerShell repository. This tutorial works on Windows, macOS and Linux.

Installing Pester​

Install from the PowerShell Gallery:

Install-Module -Name Pester -Force

On Windows you may already have Pester 3.4.0 installed — it ships with the operating system. That version cannot be updated in place, and it is different enough from v6 that following this tutorial with it will not work. If Install-Module complains about an existing installation, the installation guide covers the exact commands to get around it.

Confirming the version​

This is the step worth doing carefully. Importing the module and asking it what it is beats trusting what you think you installed:

Import-Module Pester -PassThru
ModuleType Version    PreRelease Name
---------- -------    ---------- ----
Script     6.0.0                 Pester

If the version shown starts with a 6, you are ready.

An old Pester can be loaded without you asking

PowerShell loads a module automatically the first time you call one of its commands, and it picks the highest version it can find — but if an older Pester is already loaded in your session, it stays loaded. If the version above is not what you expect, open a fresh PowerShell session and check again before doing anything else.

An editor​

Any editor will do, but Visual Studio Code with the PowerShell extension gives you the best experience: it discovers your tests as you write them and lets you run or debug a single test without leaving the file.

The VS Code page has the setup details. It is genuinely optional — everything in this tutorial is done from the terminal and works the same way regardless of what you type it in.

A folder to work in​

Create somewhere to build the module and move into it:

New-Item -Path ./pester-tutorial -ItemType Directory
Set-Location ./pester-tutorial

Every path in this tutorial is relative to that folder.

Before you move on

0/4

That is the setup done. Next you will create the Planetarium module itself.