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|
Feature: Contract tests with stubs
Whenever you stub any method, a contract is specified on the input/output values of that method.
When stubbing using the short syntax:
fake(:fake_name, method_name: :return_value)
the contract can only be specified on the return value.
The longer syntax:
stub(fake).method_name(args) { :return_value }
will also create a contract on the method input parameters.
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
stub(library).has_book?("Moby Dick") { true }
student.read("Moby Dick", library)
expect(library).to have_received.checkout("Moby Dick")
end
it "does not check out the book from library if not available" do
student = Student.new
stub(library).has_book?("Moby Dick") { false }
student.read("Moby Dick", library)
expect(library).not_to have_received.checkout("Moby Dick")
end
end
"""
Scenario: Fails when stubbed 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")
expect(library.has_book?("Moby Dick")).to be_false
end
end
"""
Scenario: Verifies that stubbed methods are called
Then spec file with following content should pass:
"""ruby
require_relative 'library'
describe Library do
verify_contract(:library)
let(:library) { described_class.new }
it "allows checking out books that are in the inventory" do
library.return("Moby Dick")
expect(library.has_book?("Moby Dick")).to be_true
end
it "does not allow checking out unavailable books" do
expect(library.has_book?("Moby Dick")).to be_false
end
it "marks books as unavailable after they are checked out" do
library.return("Moby Dick")
library.checkout("Moby Dick")
expect(library.has_book?("Moby Dick")).to be_false
end
end
"""
|
