What it does
Pester is a testing and mocking framework for PowerShell scripts, commands, modules, and functions. Tests commonly use `Describe`, `Context`, `It`, and `Should` blocks, while mocks can replace commands used by the code under test. The framework can also produce code-coverage and test-result artifacts for CI. It suits PowerShell maintainers who need repeatable checks for scripts or system configuration, provided their tests run in a supported PowerShell environment.
A Pester test begins with a PowerShell test file, typically named with the *.Tests.ps1 convention. The quick-start guide introduces Describe, Context, and It to organize cases, then uses Should assertions to check behavior. For a script that writes files, the TestDrive PSDrive can keep test file operations inside a temporary location scoped to a Describe or Context block. Pester can also mock commands so a test can check how the script responds without calling the real dependency. These are documented patterns, not tests run for this record.
Pester is installed as a PowerShell module, and the official guide uses Install-Module. The docs list compatibility with Windows PowerShell 5.1 and PowerShell 7.4 or newer; the latter runs on Windows, macOS, and Linux. Once tests are in place, Pester can emit coverage and test-result artifacts that a CI pipeline can collect.
The framework does not supply the expected behavior or assertions: the test author must decide what a script should do and which commands need to be mocked. Its official repository publishes the project under Apache License 2.0.
Strengths
- Combines PowerShell test structure, assertions, and mocking for scripts, functions, modules, and commands.
- TestDrive offers a temporary, block-scoped PowerShell drive for isolating file operations.
- The documentation describes code-coverage and test-result artifacts for CI workflows.
Watch out for
- Pester requires a supported PowerShell runtime, currently Windows PowerShell 5.1 or PowerShell 7.4 and above.
- Test authors still need to define assertions and isolate non-file side effects such as external services or commands.
Best for
- PowerShell developers testing scripts, modules, and reusable functions
- Operations teams validating deployment scripts or configuration changes
- CI jobs that need PowerShell test and coverage result files
Sources
- Quick Start | Pester (Oct 25, 2026)
- Installation and Update | Pester (Oct 25, 2026)
- Isolating File Operations using the TestDrive | Pester (Oct 25, 2026)
- Apache License, Version 2.0 (Oct 25, 2026)