Unit Testing

• The process of testing individual units of code separately from each other
• By running unit tests, it is easier to isolate what units of code are to blame for bugs.
• Unit tests are considered "white box" tests because they involve looking at the internals of an application's code and runtime.

What do we need to know to write a unit test?

• The unit we are testing (usually a function or method)
• The test cases we will create to prove the unit functions as expected
  • Inputs
    • Equivalance classes: groups of inputs that should result in similar behaviors
    • Boundary cases: values on the edges of these classes
  • Expected outputs and side effects

Unit Testing Tips

• Try to test with as many equivalance classes of inputs as possible.
• Start by focusing on tests for individual methods and functions.
• Share common setup between unit tests.

Test Case Example

What should our test cases be?

def palindrome?(word)
  word == word.reverse
end

Unit Testing with Minitest

require 'minitest/autorun'

class TestPalindrome < Minitest::Test
  def test_palindrome
    assert_true palindrome? ''
    assert_true palindrome? 'c'
    assert_false palindrome? 'car'
    assert_true palindrome? 'racecar'
    assert_false palindrome? nil
  end
end

Minitest Results

$ ruby test_palindrome.rb
Run options: --seed 65310

# Running:

E

Finished in 0.001653s, 604.7796 runs/s, 2419.1183 assertions/s.

  1) Error:
TestPalindrome#test_palindrome:
NoMethodError: undefined method `reverse' for nil:NilClass
    /Users/nick/testing-talk/palindrome.rb:2:in `palindrome?'
    test_palindrome.rb:10:in `test_palindrome'

1 runs, 4 assertions, 0 failures, 1 errors, 0 skips

Unit Testing with RSpec

describe 'palindrome?' do
  context 'given an empty string' do
    it 'returns true' do
      expect(palindrome? '').to be true
    end
  end

  context 'given a string with only one character' do
    it 'returns true' do
      expect(palindrome? 'c').to be true
    end
  end

  context 'given a longer non-palindrome' do
    it 'returns true' do
      expect(palindrome? 'car').to be false
    end
  end

  context 'given a longer palindrome' do
    it 'returns true' do
      expect(palindrome? 'racecar').to be true
    end
  end

  context 'given a null value' do
    it 'returns false' do
      expect(palindrome? nil).to be false
    end
  end
end

Acceptance Testing

• The process of testing a program's features to ensure that they meet customer requirements
• Acceptance tests give us a way to prove that software meets needs and works from a user's perspective.
• Acceptance tests are considered "black box" tests because they simulate user actions without requiring access to an application's internals (however, they can still be automated).

Testing and Process

• Depending on a project's process model and personal development practices, testing may happen after, during, or even before development.
• Waiting to test until after all development is done (waterfall) can cause difficulties with integrating work and verifying if systems themselves or their dependencies are broken.

Test Driven Development

The process of writing test code before implementation code.

Behavioral Driven Development

Similar to test driven development, but involving more process and abstraction. Tests (usually acceptance tests) are written to verify specific user stories as they are implemented.