expect_change.feature

Feature: expect change

Expect some code (wrapped in a proc) to change the state of some object.

Scenario: expecting change
  Given a file named "expect_change.rb" with:
    """
    class Counter
      class << self
        def increment
          @count ||= 0
          @count += 1
        end

        def count
          @count ||= 0
        end
      end
    end

    describe Counter, "#increment" do
      it "should increment the count" do
        expect{Counter.increment}.to change{Counter.count}.from(0).to(1)
      end

      # deliberate failure
      it "should increment the count by 2" do
        expect{Counter.increment}.to change{Counter.count}.by(2)
      end
    end
    """
  When I run "spec expect_change.rb"
  Then the stdout should match "2 examples, 1 failure"
  Then the stdout should match "should have been changed by 2, but was changed by 1"

Scenario: expecting no change
  Given a file named "expect_no_change.rb" with:
    """
    class Counter
      class << self
        def increment
          @count ||= 0
          @count += 1
        end

        def count
          @count ||= 0
        end
      end
    end

    describe Counter, "#increment" do
      it "should not increment the count by 2" do
        expect{Counter.increment}.to_not change{Counter.count}.from(0).to(2)
      end

      # deliberate failure
      it "should not increment the count by 1" do
        expect{Counter.increment}.to_not change{Counter.count}.by(1)
      end
    end
    """
  When I run "spec expect_no_change.rb"
  Then the stdout should match "2 examples, 1 failure"
  Then the stdout should match "should not have changed, but did change from 1 to 2"