TOPICPesterSYNOPSISPester is a BDD based test runner for PowerShell.DESCRIPTIONPester provides a framework for running Unit Tests to execute and validate Powershell commands. Pester follows a file naming convention for naming tests to be discovered by pester at test time and a simple set of functions that expose a Testing DSL for isolating, running, evaluating and reporting the results of Powershell commands.Pester tests can execute any command or script that is accesible to a pester test file. This can include functions, Cmdlets, Modules and scripts. Pester can be run in ad hoc style in a console or it can be integrated into the Build scripts of a Continuous Integration system.Pester also contains a powerful set of Mocking Functions that allow tests to mimic and mock the functionality of any command inside of a piece of powershell code being tested. See about_Mocking.CREATING A PESTER TESTTo start using Pester, You may use the Add-Fixture function to scaffold both a new implementation function and a test function.C:\PS>New-Fixture deploy CleanCreates two files:./deploy/Clean.ps1function clean {} ./deploy/clean.Tests.ps1 $here = Split-Path -Parent $MyInvocation.MyCommand.Path $sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path).Replace(".Tests.", ".") . "$here\$sut" Describe "clean" { It "does something useful" { $true | should be $false } } Now you have a skeleton of a clean function with a failing test. Pester considers all files containing *Tests.ps1 to be a test file (see Invoke-Pester) and by default it will look for these files and run all Describe blocks inside the file (See Describe). The Describe block can contain several behavior validations expressed in It blocks (see It). Each It block should test one thing and throw an exception if the test fails. Pester will consider any It block that throws an exception to be a failed test. Pester provides a set of extensions that can perform various comparisons between the values emited or altered by a test and an expected value (see about_Should). RUNNNING A PESTER TESTOnce you have some logic that you are ready to test, run the Tests file directly, usually by pressing F5 in your ISE. To run multiple test files, get summary for the test run, to get nUnit compatible XMLreport or to get PesterResult object use the Invoke-Pester command. You can zero in on just one test (Describe block) or an entire tree of directories.function BuildIfChanged {$thisVersion=Get-Version$nextVersion=Get-NextVersionif($thisVersion -ne $nextVersion) {Build $nextVersion}return $nextVersion}$here = Split-Path -Parent $MyInvocation.MyCommand.Path $sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path).Replace(".Tests.", ".") . "$here\$sut" Describe "BuildIfChanged" { Context "When there are Changes" { Mock Get-Version {return 1.1} Mock Get-NextVersion {return 1.2} Mock Build {} -Verifiable -ParameterFilter {$version -eq 1.2} $result = BuildIfChanged It "Builds the next version" { Assert-VerifiableMocks } It "returns the next version number" { $result | Should Be 1.2 } } Context "When there are no Changes" { Mock Get-Version -MockWith {return 1.1} Mock Get-NextVersion -MockWith {return 1.1} Mock Build {} $result = BuildIfChanged It "Should not build the next version" { Assert-MockCalled Build -Times 0 -ParameterFilter{$version -eq 1.1} } } }C:\PS>Invoke-PesterThis will run all tests recursively from the current directory downwards and print a report of all failing and passing tests to the console.PESTER AND CONTINUOUS INTEGRATIONPester integrates well with almost any build automation solution. You could create a MSBuild target that calls Pester's convenience Batch file:

This will start a powershell session, import the Pester Module and call invoke pester within the current directory. If any test fails, it will return an exit code equal to the number of failed tests and all test results will be saved to Test.xml using NUnit's Schema allowing you to plug these results nicely into most Build systems like CruiseControl, TeamCity, TFS or Jenkins.OTHER EXAMPLESPester's own tests. See all files in the Pester Functions folder containing *Tests.ps1Chocolatey tests. Chocolatey is a popular powershell based Windows package management system. It uses Pester tests to validate its own functionality.SEE ALSOabout_MockingDescribeContextItAdd-FixtureInvoke-Pesterabout_Shouldabout_TestDrive