Pester Migration

What it does

When your agent uses it

• The user asks to upgrade
• Modernize Pester tests
• Fix .Tests.ps1 files that broke after bumping the Pester version
• Convert legacy Should / Invoke-Pester syntax

Example prompts

• “/pester-migration”

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

1. 1Baseline. Run the suite on the current version first and record pass/fail. You need a
2. 2Read the reference for this jump (table above) so you know the full scope before editing.
3. 3Edit file by file. Apply the mechanical changes (see per-jump cheat sheets below and in the
4. 4Switch versions with Install-Module (Step 0), then re-import: `Remove-Module Pester;
5. 5Run and fix. Re-run with -Output Detailed; use -Output Diagnostic (v4→v5) or read the
6. 6Green, diff, commit. Re-run until the result matches the baseline (or better). Review the

What it can do on your machine

Read from SKILL.md and the folder at commit 727ff2e. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • git

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • pester.dev

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Pester Migration loads about 2.1k tokens when it runs, and up to ~8.5k if it reads all its reference files. Until then it costs about 151 tokens; SKILL.md has 720 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~151

When it runs · the whole SKILL.md, loaded when a task matches

~2.1k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~8.5k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from github/awesome-copilot at commit 727ff2e, republished under its MIT licence (© github). 720 words, ~2,058 tokens.

name

pester-migration

description

Pester migration skill for upgrading PowerShell Pester test suites across major versions — v3→v4, v4→v5, and v5→v6. Covers the Discovery/Run two-phase model, moving setup into BeforeAll, $PSScriptRoot vs $MyInvocation, mock changes (Assert-MockCalled → Should -Invoke, removed fall-through), Invoke-Pester parameters → PesterConfiguration, data-driven -ForEach/-TestCases, and the v6 breaking changes. Use when the user asks to upgrade, migrate, or modernize Pester tests, fix *.Tests.ps1 files that broke after bumping the Pester version, or convert legacy Should / Invoke-Pester syntax.

# Installed Pester version(s) on this machine
Get-Module Pester -ListAvailable | Select-Object Name, Version, Path

# Version currently imported in the session
(Get-Module Pester).Version

# Latest stable v5 — pin the major to avoid installing Pester 6
Install-Module Pester -MaximumVersion 5.99.99 -Force

# Pester 6
Install-Module Pester -Force

# 1. Move file import into BeforeAll, use $PSScriptRoot (NOT $MyInvocation.MyCommand.Path)
# BEFORE
$here = Split-Path -Parent $MyInvocation.MyCommand.Path
. "$here\Get-Thing.ps1"
# AFTER
BeforeAll { . $PSScriptRoot/Get-Thing.ps1 }

# 2. Any code that DISCOVERS/generates tests must be in BeforeDiscovery
BeforeDiscovery { $cases = Get-Content $PSScriptRoot/cases.json | ConvertFrom-Json }

# 3. Should -Throw matches with -like wildcards, not .Contains
{ throw 'a long message' } | Should -Throw '*long*'

# 4. Invoke-Pester legacy params → New-PesterConfiguration (see reference for full map)

# 1. Mock assertions: removed verbs — rename (old -> new):
#    Assert-MockCalled     -> Should -Invoke
#    Assert-VerifiableMock -> Should -InvokeVerifiable
Should -Invoke Get-Thing -Times 1 -Exactly
Should -InvokeVerifiable

# 2. Add a default mock — unmatched calls no longer run the real command
Mock Get-Thing { 'default' }
Mock Get-Thing -ParameterFilter { $Name -eq 'a' } -MockWith { 'a' }

# 3. Empty/$null -ForEach now throws; allow it only where empty is expected
Describe 'Optional' -ForEach $cases -AllowNullOrEmptyForEach { }

# 4. Combine duplicate BeforeAll/BeforeEach/AfterAll/AfterEach in the same block into one

© github, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 3 other files (references) in skills/pester-migration of github/awesome-copilot.

• SKILL.md
• references/v3-to-v4.md
• references/v4-to-v5.md
• references/v5-to-v6.md

Open the folder on GitHubat commit 727ff2e