unit-testing.md

Unit Testing

How do you write hard to test code?

Hard to answer but easy to do. Do it intrinsically.

Most people say:

• Make things private
• Using final keyword
• Long methods
• ...

Real issues:

• Mixing new with logic
• looking for things
• Work in constructor
• Global state
• Singleton
• Static methods (No seam)
• Deep inheritance

Writing testable code

• Good OO
• Dependency Injection
• Test Driven Development
• A whole lot about un-testable code

There is no secret to writing test... there are only secrets to writing testable code!

Different kind of tesets

• Scenario/Large tests
• • Test whole application by pretending to be a user
• • Slow/Flaky/Mostly happy paths
• Functional/Medium Tests
• • External dependencies simulated
• • Test class interaction -Unit/Small tests
• • Focus on application logic
• • Very Fast/ No I/O / No need for a debugger

Hard to test code: Mix object creation code and business logic.

This will assure that a test can never construct a graph of objects different from production. Hence nothing can be tested in isolation.

Take Away

• Unit tests are a preferred way of testing
• Unit tests require separation of instantiation of object graph from business logic under test