unit_test_summary.rb

unit_test_summary.rb

# 1. Pure leaf function: test critical values and noncritical regions
it 'occurs when multiple of 4 but not 100' do
  expect(leap?(2008)).to be_truthy
end
it 'does not occur when multiple of 400' do
  expect(leap?(2000)).to be_falsy
end

# 2. Using doubles for explicit dependencies such as collaborators
#    UI.background() calls Defcon.level() to determine display color
it 'colors the UI red if Defcon is 2 or lower' do
  # Arrange: stub Defcon to return 2
  allow(Defcon).to receive(:level).and_return(2)  
  expect(UI.background).to eq('red')        # Act and Assert
end

# 3. Has implicit dependencies such as time
it 'runs backups on Tuesdays' do
  # Arrange: stub Date.today to return Tues 2020-02-04
  allow(Date).to receive(:today).and_return(Time.local(2020,2,4))
  expect(run_backups_today?()).to be_truthy  # Act and Assert
end

# 4. Has side effects (verbose version)
it 'lowers Defcon level by 1' do
  # Arrange: check previous value of state
  before = Defcon.level()
  post_alert("Hostile craft detected")    # Act
  expect(Defcon.level()).to eq(before - 1) # Asset
end

# Shortcut version passing a callable to `expect`
it 'lowers Defcon level by 1' do
  expect { post_alert("Hostile craft detected") }.
    to change { Defcon.level() }.by(-1)
end