Ruby Mocking and Stubbing

Mocking and stubbing are essential techniques in Ruby for creating effective unit tests. These methods allow developers to isolate code, simulate behavior, and improve test reliability.

What are Mocking and Stubbing?

Mocking creates objects that mimic the behavior of real objects in controlled ways. Stubbing, on the other hand, replaces specific method behaviors with predefined responses.

Why Use Mocking and Stubbing?

• Isolate code under test
• Simulate complex scenarios
• Speed up test execution
• Test error handling

Mocking in Ruby

Ruby provides several libraries for mocking, with RSpec being one of the most popular. Here's a simple example using RSpec:

require 'rspec'

class WeatherService
  def get_temperature(city)
    # Imagine this method makes an API call
  end
end

describe WeatherService do
  it "returns the temperature for a city" do
    weather_service = instance_double(WeatherService)
    allow(weather_service).to receive(:get_temperature).with("London").and_return(20)

    expect(weather_service.get_temperature("London")).to eq(20)
  end
end
    

In this example, we create a mock object using instance_double and define its behavior using allow.

Stubbing in Ruby

Stubbing is often used to replace method calls with predefined return values. Here's an example:

require 'rspec'

class User
  def full_name
    "John Doe"
  end
end

describe User do
  it "returns a stubbed full name" do
    user = User.new
    allow(user).to receive(:full_name).and_return("Jane Smith")

    expect(user.full_name).to eq("Jane Smith")
  end
end
    

This code demonstrates how to stub the full_name method to return a different value during testing.

Best Practices

• Only mock or stub what's necessary
• Use mocks for behavior verification
• Use stubs for state verification
• Keep mocks and stubs simple
• Avoid mocking third-party code

Related Concepts

To further enhance your Ruby testing skills, explore these related topics:

• Ruby Unit Testing
• Ruby RSpec Basics
• Ruby Test::Unit Framework

By mastering mocking and stubbing, you'll be able to write more robust and reliable tests for your Ruby applications. Remember to use these techniques judiciously and always aim for clear, maintainable test code.