02_structure.md

What does an RSpec test look like?

describe 'some class name' do
  it 'works correctly' do
    expect(1 + 1).to eq 2
  end
end

Note: describe is used to set up the RSpec test and gives us access to the RSpec DSL it is a function that takes a description and a block (which is the actual test)

Great! We have RSpec up and working, let's test a method

class TestClass
  def add_one_to(num)
    num + 1
  end
end

describe TestClass do
  it 'works correctly' do
    # Setup
    class = TestClass.new
    
    # Exercise
    result = class.add_one_to(1)
  
    # Verify
    expect(result).to eq 2
  end
end

class TestClass
  def add_one_to(num)
    num + 1
  end
end

describe TestClass do
  it 'works correctly' do
    expect(subject.add_one_to(1)).to eq 2
  end
end

...where did subject come from?

subject is an RSpec helper that creates a new object of the class being described

How do we know a test is passing for the reason I expect?

A common practice is to make a test fail by changing the expectation

Note: This also let's us be sure the test will fail if something changes

What if my test needs more context than I can put in a single line?

context

class TestClass
  def add_one_to(num)
    num + 1
  end
end

describe TestClass do
  context 'when adding one to one' do
    it 'works correctly' do
      expect(subject.add_one_to(1)).to eq 2
    end
  end
end

Note: Like describe and it, context is also a function that takes a description and a block You can also nest contexts and describes as deeply as you'd like It's common to try to make the contexts and describes read well when read together because of how it's ouput from the console

Neat, what if I need to set up some conditions for my test?

That's what a before does!

class TestClass
  def add_one_to(num)
    num + 1
  end
end

describe TestClass do
  context 'when adding one to one' do
    before do
      @num = 1
    end

    it 'works correctly' do
      expect(subject.add_one_to(@num)).to eq 2
    end
  end
end

Note: A before can be used to do more useful things like log in as a user or navigate to a page

Be careful though! Notice how in the context of the spec, we don't know what @num is

it 'works correctly' do
  expect(subject.add_one_to(@num)).to eq 2
end

Note: This is called a "Mystery Guest". In this case it's harmless, but imagine if this was line 300+ of a large spec file with lots of let and before blocks.

Okay, how about if I need data for my test?

let and let!

class TestClass
  def add_one_to(num)
    num + 1
  end
end

describe TestClass do
  context 'when adding one to one' do
    let(:num) { 1 }

    it 'works correctly' do
      expect(subject.add_one_to(num)).to eq 2
    end
  end
end

Note: The difference between let and let! is that the let! will be run no matter what, where regular let isn't evaluated until it's used

Next Steps