Why and What to Test

Why and What to Test

In this lesson — part of Testing Fundamentals — you'll learn why and what to test in PowerShell and why it matters in real work.

Why it matters

Tests prove your code works and keep it working as you change it.

Key ideas

• What to test
• Arrange-Act-Assert
• Running a test suite
• Good vs. brittle tests

In practice

Here's how it looks in idiomatic PowerShell:

# requires the Pester module
Describe 'Add-Numbers' {
    BeforeAll { function Add-Numbers($a, $b) { $a + $b } }

    It 'sums two integers' {
        Add-Numbers 2 3 | Should -Be 5
    }
    It 'throws on null' {
        { Add-Numbers $null } | Should -Throw
    }
}
# run with: Invoke-Pester

PowerShell note: Pester is PowerShell's de facto test framework with a Describe/It/Should DSL, and its Should -Throw assertion requires the code under test to be wrapped in a script block { } so the failure is caught rather than thrown at parse/run time.

Try it yourself

Exercise: In PowerShell, write three tests for a function that reverses a string.

Recap

You now understand why and what to test and can apply it in PowerShell. Mark this lesson complete and continue to the next one.