1. Best practices for writing
automated tests
Felipe Lima
felipe@gogobot.com
@felipecsl

2. • Assumption 1: You are already
convinced that automated tests are
good

3. • Assumption II: You agree that best
way to accomplish that is writing
tests before you code.

4. What is considered to be a
good test?

5. Structure - AAA:
• Arrange
• Act
• Assert

7. What makes a good test?

8. • Assumes a clean environment (empty
database, redis, solr, etc.)
• Cleans up after itself
• Runs quickly
• Readable, simple to understand
• Tests only one thing at a time

9. • Isolates the class you are testing
• Stubs external dependencies (eg.: vcr)
• Thorough: covers happy and edge cases
• Repeatable: always provides same results
• Doesn’t make unnecessary assertions
• Clearly and consistently named

10. SOLID
• Single Responsibility Principle
• Open/closed principle
• Liskov substitution principle
• Interface segregation principle
• Dependancy Inversion principle

11. Why write tests before the code?

12. • SOLID code is HIGHLY testable
• TDD forces you to think about your
design
• Bad code is hard to test
• It is a design process, not a testing process

13. “TDD is a robust way of designing
software components (“units”)
interactively so that their behaviour is
specified through unit tests.”
http://blog.stevensanderson.com/2009/08/24/writing-great-unit-tests-best-and-worst-practises/

14. http://blog.stevensanderson.com/2009/08/24/writing-great-unit-tests-best-and-worst-practises/

15. TDD Mantra:
Red => Green => Refactor
http://www.agileapps.co.uk/methodology/continuous.html

16. Mocks and Stubs:
• Mocks set up expectations on messages that
are passed between objects
• Stubs provide canned answers to calls made
during the test
• Only mocks specify expected behavior and
make assertions
• Also know as test doubles (eg.: in RSpec)
Reference: http://martinfowler.com/articles/mocksArentStubs.html

17. Stub example:
controller.stub(:current_user).and_return(fake_user)
Mock example:
user.should_receive(:postcards).and_return([p1, p2, p3])
postcards = controller.postcards(user.id)
postcards.should =~ [p1, p2, p3]