Powershell-Pester-5

# PowerShell Pester v5 Testing Guidelines

This guide provides PowerShell-specific instructions for creating automated tests using PowerShell Pester v5 module. Follow PowerShell cmdlet development guidelines in [powershell.instructions.md](./powershell.instructions.md) for general PowerShell scripting best practices.

File Naming and Structure

- **File Convention:** Use `*.Tests.ps1` naming pattern

- **Placement:** Place test files next to tested code or in dedicated test directories

- **Import Pattern:** Use `BeforeAll { . $PSScriptRoot/FunctionName.ps1 }` to import tested functions

- **No Direct Code:** Put ALL code inside Pester blocks (`BeforeAll`, `Describe`, `Context`, `It`, etc.)

Test Structure Hierarchy

BeforeAll { # Import tested functions }
Describe 'FunctionName' {
    Context 'When condition' {
        BeforeAll { # Setup for context }
        It 'Should behavior' { # Individual test }
        AfterAll { # Cleanup for context }
    }
}

Core Keywords

- **`Describe`**: Top-level grouping, typically named after function being tested

- **`Context`**: Sub-grouping within Describe for specific scenarios

- **`It`**: Individual test cases, use descriptive names

- **`Should`**: Assertion keyword for test validation

- **`BeforeAll/AfterAll`**: Setup/teardown once per block

- **`BeforeEach/AfterEach`**: Setup/teardown before/after each test

Setup and Teardown

- **`BeforeAll`**: Runs once at start of containing block, use for expensive operations

- **`BeforeEach`**: Runs before every `It` in block, use for test-specific setup

- **`AfterEach`**: Runs after every `It`, guaranteed even if test fails

- **`AfterAll`**: Runs once at end of block, use for cleanup

- **Variable Scoping**: `BeforeAll` variables available to child blocks (read-only), `BeforeEach/It/AfterEach` share same scope

Assertions (Should)

- **Basic Comparisons**: `-Be`, `-BeExactly`, `-Not -Be`

- **Collections**: `-Contain`, `-BeIn`, `-HaveCount`

- **Numeric**: `-BeGreaterThan`, `-BeLessThan`, `-BeGreaterOrEqual`

- **Strings**: `-Match`, `-Like`, `-BeNullOrEmpty`

- **Types**: `-BeOfType`, `-BeTrue`, `-BeFalse`

- **Files**: `-Exist`, `-FileContentMatch`

- **Exceptions**: `-Throw`, `-Not -Throw`

Mocking

- **`Mock CommandName { ScriptBlock }`**: Replace command behavior

- **`-ParameterFilter`**: Mock only when parameters match condition

- **`-Verifiable`**: Mark mock as requiring verification

- **`Should -Invoke`**: Verify mock was called specific number of times

- **`Should -InvokeVerifiable`**: Verify all verifiable mocks were called

- **Scope**: Mocks default to containing block scope

Mock Get-Service { @{ Status = 'Running' } } -ParameterFilter { $Name -eq 'TestService' }
Should -Invoke Get-Service -Exactly 1 -ParameterFilter { $Name -eq 'TestService' }

Test Cases (Data-Driven Tests)

Use `-TestCases` or `-ForEach` for parameterized tests:

It 'Should return <Expected> for <Input>' -TestCases @(
    @{ Input = 'value1'; Expected = 'result1' }
    @{ Input = 'value2'; Expected = 'result2' }
) {
    Get-Function $Input | Should -Be $Expected
}

Data-Driven Tests

- **`-ForEach`**: Available on `Describe`, `Context`, and `It` for generating multiple tests from data

- **`-TestCases`**: Alias for `-ForEach` on `It` blocks (backwards compatibility)

- **Hashtable Data**: Each item defines variables available in test (e.g., `@{ Name = 'value'; Expected = 'result' }`)

- **Array Data**: Uses `$_` variable for current item

- **Templates**: Use `<variablename>` in test names for dynamic expansion

# Hashtable approach
It 'Returns <Expected> for <Name>' -ForEach @(
    @{ Name = 'test1'; Expected = 'result1' }
    @{ Name = 'test2'; Expected = 'result2' }
) { Get-Function $Name | Should -Be $Expected }

# Array approach
It 'Contains <_>' -ForEach 'item1', 'item2' { Get-Collection | Should -Contain $_ }

Tags

- **Available on**: `Describe`, `Context`, and `It` block