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 Ruby 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 Ruby:

require "minitest/autorun"

class TestMath < Minitest::Test
  def test_addition
    assert_equal 4, 2 + 2
    refute_equal 5, 2 + 2
  end
end

Ruby note: Minitest ships with Ruby: subclass Minitest::Test, name methods test_*, and require "minitest/autorun" auto-runs them with assertions like assert_equal.

Try it yourself

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

Recap

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