Pester

Pester is an open-source testing framework for PowerShell governed by the Pester core team and community contributors under OpenCollective and GitHub Sponsors funding. Pester provides a domain-specific language (DSL) for writing, executing, and reporting automated unit, functional, and integration tests across PowerShell scripts, functions, modules, and infrastructure configurations.

Syntax, Discovery, & Execution

Pester structures tests using block-level keywords (Describe, Context, It, BeforeAll, AfterAll) and an assertion library (Should) designed for test readability. The framework handles test file discovery (matching *.Tests.ps1 naming conventions), test execution, and terminal diff reporting without requiring third-party testing harnesses.

Mocking & Code Coverage

The framework incorporates built-in command mocking capabilities that intercept PowerShell cmdlets, functions, and external commands, allowing developers to control return values and assert call counts without altering production code dependencies or requiring object-oriented dependency injection frameworks. Pester tracks line-level code execution during test runs and generates code coverage reports in industry-standard formats, including JaCoCo and Cobertura.

Cross-Platform & CI/CD Integration

Pester executes on PowerShell 7.4+ across Windows, macOS, and Linux operating systems. The framework integrates with Visual Studio Code via the PowerShell extension and exports test results in NUnit and JUnit XML formats for integration into CI/CD build pipelines, including GitHub Actions, Azure Pipelines, and Jenkins.