Pester Testing Test Guide

Running Pester Tests

Go to the top level of the PowerShell repository and run: Start-PSPester inside a self-hosted copy of PowerShell.

You can use Start-PSPester -Tests SomeTestSuite* to limit the tests run.

Testing new `powershell` processes

Any launch of a new powershell process must include -noprofile so that modified user and system profiles do not causes tests to fail. You also must take care to call the development copy of PowerShell, which is not the first one on the path.

Example:

    $powershell = Join-Path -Path $PsHome -ChildPath "powershell"
    & $powershell -noprofile -command "ExampleCommand" | Should Be "ExampleOutput"

Portability

Some tests simply must be tied to certain platforms. Use Pester's -Skip directive on an It statement to do this. For instance to run the test only on Windows:

It "Should do something on Windows" -Skip:($IsLinux -Or $IsOSX) { ... }

Or only on Linux and OS X:

It "Should do something on Linux" -Skip:$IsWindows { ... }

Pending

When writing a test that should pass, but does not, please do not skip or delete the test, but use It "Should Pass" -Pending to mark the test as pending, and file an issue on GitHub.

Who this is for

Cmdlet behavior is validated using the Pester testing framework. The purpose of this document is to create a single standard to maximize unit test coverage while minimizing confusion on expectations. What follows is a working document intended to guide those writing Pester unit tests for PowerShell.

Unit testing is done not only to validate that the block of code works as expected, but also to assist the developer to know precisely where in the code to look; in some cases, seeing the source code may inspire better unit tests. In many cases, a unit test is the only documented specification. Fortunately, the MSDN is a great source of information about Cmdlets.

Test suites need to be created and many cmdlets added and unit-tested. The following list is to be used to guide the thought process of the developer in writing a suite in minimal time, while enhancing quality.

Test suites should proceed as functional and system tests of the cmdlets, and the code treated as a black box for the purpose of test suite design.

Testing Standards

Readability

Every effort should be made to maximize readability of code. Code is written for the developer in the future to debug- not for the developer writing the code.

When assertions are on consecutive lines, the pipes should line up:

MyFirstCondition | Should Be 0
MySecondCondition | Should Be 1

This is less readable than:

MyFirstCondition  | Should Be 0
MySecondCondition | Should Be 1

So the second section of code should instead be used. The same style should be followed for assignments of variables on consecutive lines:

$var1 = <expression 1>
$variable2 = <expression 2>
$var3 = <expression 3>
$typeCollection1 = <expression 4>
$object1 = <expression>
... etc

is much less readable than

$var1            = <expression 1>
$variable2       = <expression 2>
$var3            = <expression 3>
$typeCollection1 = <expression 4>
$object1         = <expression 5>
... etc

So all assignment statements must be aligned.

Other style standards are no less important to readability of the code:

Use readable and meaningful variable name when assigning variables.
Do not make large functions. Tests should be simple: define -> manipulate -> assert
Do not use tabs. Tabs are rendered differently depending upon the machine. This greatly affects readability.
Remove the first 3 auto-generated lines of each .Tests.ps1 file. This is created automatically by Pester and is unnecessary. Each .Test.ps1 file should begin with a Describe block.
Discard the auto-generated function file that is generated in tandem with the .Tests.ps1 file
Name the test file "Test- when you create a new test fixture.
Each test describes a behavior- use the word "Should" at the beginning of each test description- so it reads "It 'Should..."

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