Pester is a unit test framework for PowerShell. It provides a domain specific language that allows you to define test cases. It is also used to perform operational/infrastructure testing and this is encouraged by Microsoft who leverage Pester as part of the Operation Validation Framework project.
Per the Pester project page:
Pester provides a framework for running unit tests to execute and validate PowerShell commands from within PowerShell. Pester consists of a simple set of functions that expose a testing domain-specific language (DSL) for isolating, running, evaluating and reporting the results of PowerShell commands.
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