Feature: Contract tests with mocks Whenever you mock something, you specify a contract on the arguments/return value pair. Bogus can check automatically whether this contract was satisfied. Background: Given a file named "library.rb" with: """ruby class Library def initialize @books = [] end def has_book?(book) @books.include?(book) end def checkout(book) @books.delete(book) end def return(book) @books << book end end """ Given a file named "student.rb" with: """ruby class Student def read(book, library = Library.new) if library.has_book?(book) library.checkout(book) end end end """ And a spec file named "student_spec.rb" with: """ruby require_relative 'student' require_relative 'library' describe Student do fake(:library) it "checks out the book from library if it is available" do student = Student.new mock(library).has_book?("Moby Dick") { true } mock(library).checkout("Moby Dick") { "Moby Dick" } student.read("Moby Dick", library) end it "does not check out the book from library if not available" do student = Student.new mock(library).has_book?("Moby Dick") { false } student.read("Moby Dick", library) library.should_not have_received.checkout("Moby Dick") end end """ Scenario: Fails when mocked methods are not called on real object Then spec file with following content should fail: """ruby require_relative 'library' describe Library do verify_contract(:library) let(:library) { Library.new } it "marks books as unavailable after they are checked out" do library.return("Moby Dick") library.checkout("Moby Dick") library.has_book?("Moby Dick").should be_false end end """ Scenario: Verifies that mocked methods are called Then spec file with following content should pass: """ruby require_relative 'library' describe Library do verify_contract(:library) let(:library) { Library.new } it "allows checking out books that are in the inventory" do library.return("Moby Dick") library.has_book?("Moby Dick").should be_true end it "does not allow checking out unavailable books" do library.has_book?("Moby Dick").should be_false end it "marks books as unavailable after they are checked out" do library.return("Moby Dick") library.checkout("Moby Dick") library.has_book?("Moby Dick").should be_false end end """