Infrastructure Testing With Pester

Use PowerShell’s de facto standard unit testing module to validate your infrastructure is deployed and configured to your specifications.

What is “Infrastructure Testing”

In my own words, infrastructure testing is:

validating that a configuration item is the value that you expect it to be.

For example:

• Is the Operating System Windows Server?
• Is the DNS service running?
• Is the count of members of the local ‘Administrators’ group 3?

As a sysadmin, these are things that I would check on as part of my daily operations tasks, and also things that I would check on during troubleshooting. But as infrastructure gets larger; spanning across multiple environments, multiple layers of virtualization and multiple vendors, versions and applications it becomes too complex and time consuming to do without automation.

Pester testing module

Most programming languages have a testing library that allows the developer to write tests that validate that their code does what is expected. PowerShell is no different, and the de-facto module for those tests is Pester

Pester follows the Behavior Driven Design “specification” language; mainly the use of Describe, Context, It, and Should. These four “Domain Specific Language (DSL)” keywords allow you to write a test that sounds a lot like natural language.

here is an example straight from the Pester documentation:

BeforeAll {
    function Get-Planet ([string]$Name = '*') {
        $planets = @(
            @{ Name = 'Mercury' }
            @{ Name = 'Venus'   }
            @{ Name = 'Earth'   }
            @{ Name = 'Mars'    }
            @{ Name = 'Jupiter' }
            @{ Name = 'Saturn'  }
            @{ Name = 'Uranus'  }
            @{ Name = 'Neptune' }
        ) | ForEach-Object { [PSCustomObject] $_ }

        $planets | Where-Object { $_.Name -like $Name }
    }
}

Describe 'Get-Planet' {
    It 'Given no parameters, it lists all 8 planets' {
        $allPlanets = Get-Planet
        $allPlanets.Count | Should -Be 8
    }
}

Operations Validation Framework

One of the first modules that used Pester to test infrastructure was Operation Validation Framework. Although the project was abandoned about 3 years ago, it is still available to download from github and the powershell gallery.

With your tests organized in this way, calling Invoke-OperationValidation will run the Pester tests in the folders and produce a report of the test name and result.

See the example in the README.md

Poshspec

poshspec added some very useful terms to the DSL, such as File, Hotfix, etc. There is a list of them on the wiki. This made the tests even more like natural language.

Unfortunately, this site also stopped being updated around the same time as OVF, and has the same issues when running with Pester v5

PSRemotely

Lastly, psremotely was another PowerShell infrastructure testing module based on Pester. It also had its own DSL terms such as Nodes to describe the “target” computers to run the tests on.

Where OVF ran the tests locally, PSRemotely ran them, well …. remotely. The idea was to copy the tests and all the modules, scripts and resources required to run them to the remote system, run the tests and then retrieve the results and write them to the local machine as a json object.