TOPIC
	Pester

SYNOPSIS
	Pester is a BDD based test runner for PowerShell.

DESCRIPTION
	Pester 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 accessible 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 TEST
	To start using Pester, you may use the New-Fixture function to scaffold both 
	a new implementation function and a test function.

	C:\PS>New-Fixture deploy Clean

	Creates two files:
	./deploy/Clean.ps1
	function 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 emitted or altered by a test and an expected 
    value (see about_Should). 

RUNNNING A PESTER TEST
	Once 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 XML
	report 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
		$nextVersion=Get-NextVersion
		if($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-Pester

	This 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 INTEGRATION
	Pester integrates well with almost any build automation solution. You 
	could create a MSBuild target that calls Pester's convenience Batch file:

	<Target Name="Tests">
	<Exec Command="cmd /c $(baseDir)pester\bin\pester.bat" />
	</Target>

	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 EXAMPLES
	Pester's own tests. See all files in the Pester Functions folder 
	containing *Tests.ps1
	
	Chocolatey tests. Chocolatey is a popular PowerShell based Windows 
	package management system. It uses Pester tests to validate its own 
	functionality.

SEE ALSO
	about_Mocking
	Describe
	Context
	It
	New-Fixture
	Invoke-Pester
	about_Should
	about_TestDrive
