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Feature: Spies
Object Oriented Programming is all about messages sent between the objects. If you follow principles like "Tell, Don't Ask", you will enable yourself to combine Bogus's powerful feature of faking objects with it's ability to verify object interactions.
Typically, stubbing libraries force you to first stub a method, so that you can later make sure it was called. However, if you use fakes, Bogus lets you verify that a method was called (or not) without stubbing it first.
Background:
Given a file named "library.rb" with:
"""ruby
class Library
def checkout(book)
# marks book as checked out
end
end
"""
Given a file named "student.rb" with:
"""ruby
class Student
def initialize(library)
@library = library
end
def study(*book_titles)
book_titles.each do |book_title|
@library.checkout(book_title)
end
end
end
"""
Scenario: Ensuring methods were called
Then spec file with following content should pass:
"""ruby
require_relative 'student'
require_relative 'library'
describe Student do
fake(:library)
it "studies using books from library" do
student = Student.new(library)
student.study("Moby Dick", "Sherlock Holmes")
expect(library).to have_received.checkout("Moby Dick")
expect(library).to have_received.checkout("Sherlock Holmes")
end
end
"""
Scenario: Spying on methods that do not exist
Then spec file with following content should fail:
"""ruby
require_relative 'student'
require_relative 'library'
describe Student do
fake(:library)
it "studies using books from library" do
student = Student.new(library)
student.study("Moby Dick")
expect(library).not_to have_received.return_book("Moby Dick")
end
end
"""
Scenario: Spying on methods with wrong number of arguments
Then spec file with following content should fail:
"""ruby
require_relative 'student'
require_relative 'library'
describe Student do
fake(:library)
it "studies using books from library" do
student = Student.new(library)
student.study("Moby Dick", "Sherlock Holmes")
expect(library).not_to have_received.checkout("Moby Dick",
"Sherlock Holmes")
end
end
"""
Scenario: Spying on previously stubbed methods
Then spec file with following content should pass:
"""ruby
require_relative 'student'
require_relative 'library'
describe Student do
fake(:library)
it "studies using books from library" do
stub(library).checkout("Moby Dick") { "checked out" }
expect(library.checkout("Moby Dick")).to eq("checked out")
expect(library).to have_received.checkout("Moby Dick")
end
end
"""
Scenario: Spying on attribute writers
Given a file named "canvas.rb" with:
"""ruby
class Canvas
def background_color=(color)
# do something complicated
end
end
"""
Given a file named "popup.rb" with:
"""ruby
class Popup
def self.alert(message, canvas)
canvas.background_color = "red"
# display message
end
end
"""
Then spec file with following content should pass:
"""ruby
require_relative 'canvas'
require_relative 'popup'
describe Popup do
fake(:canvas)
it "sets the background to red" do
Popup.alert("No such file!", canvas)
expect(canvas).to have_received(:background_color=, "red")
end
end
"""
|
