unit_test_spec.rb

describe SomeClass do
  context "when defining a subject" do
    # GOOD
    # it's okay to define a `subject` here:
    subject { "foo" }

    it { should eq "foo" }
  end

  context "when using an explicit subject" do
    subject { "foo" }

    it "should equal foo" do
      # BAD
      # although it's valid RSpec code and this test passes,
      # it's not okay to use `subject` here:
      expect(subject).to eq "foo"
    end
  end

  describe ".some_class_method" do
    it "does something" do
      # ...
    end
  end

  describe "#some_instance_method" do
    it "does something" do
      expect(something).to eq "something"
    end
  end

  describe "#another_instance_method" do
    context "when in one case" do
      it "does something" do
        # ...
      end
    end

    context "when in other case" do
      it "does something else" do
        # ...
      end
    end
  end

  # Good
  # One expectation per `it`
  describe "#update" do
    it "sets the phone number" do
      expect(phone_number).to eq "+123456789"
    end

    it "sets the postal_code" do
      expect(postal_code).to eq "000000"
    end
  end

  # Bad
  # Multiple expectations per `it`
  describe "#update" do
    it "sets attributes" do
      expect(phone_number).to eq "+123456789"
      expect(postal_code).to eq "000000"
    end
  end
end