Pester: automated tests for PowerShell scripts and infrastructure

Pester is the native PowerShell testing framework, included in Windows by default and used to validate scripts, modules and infrastructure configuration. Pester tests make PowerShell scripts production-ready.

Install and basic structure

Install-Module Pester -Force -Scope CurrentUser

# Structure of a test file (Get-UserInfo.Tests.ps1)
BeforeAll {
    . "$PSScriptRoot/Get-UserInfo.ps1"  # import the script under test
}

Describe "Get-UserInfo" {
    Context "Valid user" {
        It "Returns an object with DisplayName" {
            $result = Get-UserInfo -UPN "admin@company.com"
            $result.DisplayName | Should -Not -BeNullOrEmpty
        }
        It "Returns the correct email" {
            $result = Get-UserInfo -UPN "admin@company.com"
            $result.Mail | Should -Be "admin@company.com"
        }
    }

    Context "Invalid user" {
        It "Throws an error for an invalid UPN" {
            { Get-UserInfo -UPN "doesnotexist@company.com" } | Should -Throw
        }
    }
}

Mocking — isolate external dependencies

BeforeAll { . "$PSScriptRoot/Send-Report.ps1" }

Describe "Send-Report" {
    It "Calls Send-MailMessage with the correct recipient" {
        Mock Send-MailMessage { }  # does not send a real email

        Send-Report -To "manager@company.com" -Subject "Report"

        Should -Invoke Send-MailMessage -Times 1 `
            -ParameterFilter { $To -eq "manager@company.com" }
    }
}

Azure infrastructure tests

Describe "Azure infrastructure — rg-analytics-prod" {
    BeforeAll { Connect-AzAccount -Identity }

    It "Storage Account exists" {
        Get-AzStorageAccount -ResourceGroupName "rg-analytics-prod" `
            -Name "stadatalakeprod" | Should -Not -BeNullOrEmpty
    }
    It "Key Vault has soft-delete enabled" {
        $kv = Get-AzKeyVault -VaultName "kv-bconcepts-prod"
        $kv.EnableSoftDelete | Should -Be $true
    }
}

Integrate into Azure DevOps

- task: PowerShell@2
  inputs:
    targetType: inline
    script: |
      Install-Module Pester -Force -Scope CurrentUser
      $result = Invoke-Pester -Path ./tests -PassThru
      if ($result.FailedCount -gt 0) { exit 1 }

Conclusion

PowerShell scripts without tests are a risk in production. Pester makes it trivial to write unit tests (with mocks to isolate APIs) and infrastructure tests (to validate post-deploy state). Integrate them into CI/CD pipelines to prevent regressions.