TDD / BDD

TotT 2014

TDD

Test-driven development is a short, repetitive process.

1. Write a failing test case for an enhancement (red)
2. Implement the minimum code to pass the test (green)
3. Refactor the code to meet project standards (refactor)

Benefits

• Focus on requirements
• Short development cycles
• Safety net for refactoring
• Forces thoughts about design

Use Cases

• Maximizing test coverage
• Supporting continuous integration
• Improving legacy code

But what do you test?

BDD

Behavior-driven development builds on TDD.

1. Specify desired behavior in a consistent format
2. Write a failing test case for a scenario
3. Implement the minimum code to pass the test
4. Refactor the code to meet standards

Use Cases

• Outlining required tests
• Communicating with stakeholders
• Documenting design decisions

But what is a consistent format?

One Format: Gherkin

• Domain specific language
• Business readable
• From Cucumber BDD (Ruby)
• Documents behavior
• Binds to test cases

Example: Gherkin

Feature: App store validates customer credit card

Scenario: First-time customer
  Given a customer is unknown
  When the customer checks out
  Then the checkout process should prompt for cc info
  
Secnario: Customer credit card expired
  Given a customer is known
  And the cc on-file is expired
  When the customer checks out
  Then the checkout process should prompt for new cc info
  
...

Behave

"behave is behaviour-driven development, Python style. ... [It] uses tests written in a natural language style, backed up by Python code."
- pythonhosted.org/behave

Components

• Feature files contain Gherkin scenarios
• Step files contain test code
• behave CLI binds the two

Demo: Fibonacci Numbers

Spec, test, code, refactor

Demo: Fibonacci Numbers

What about non-trivial units?

Say I have a class that uses a database?

Dependency Injection

• Make components pluggable
• In production, use real objects (e.g., database)
• In test, use "fakes" (e.g., stub database)

To Be Continued

We'll need a whole other session

Is Gherkin the only way?

Example: Mocha

describe('app store validation', function(){
  describe('first-time customer', function() {
    // test setup
    it('should prompt for cc info', function() {
      // test assertions
    });
  });
});

Review

• TDD and BDD
• Gherkin
• Behave
• Features and steps
• Mocha