Test Driven Development
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Test Driven Development (TDD) involves writing tests before code to drive the development process. It emphasizes: 1. Starting with writing an acceptance test for the thinnest slice of functionality, known as a "walking skeleton". 2. Writing unit tests by following the "write tests backwards" approach of specifying the test name, call to code, and expectations before writing code to pass the test. 3. Using mock objects to guide interface design by specifying the required services of an object rather than its provided features, promoting narrow, role-based interfaces between objects.
Test Driven Development
- 2. Why Test Driven Development ? Pair Programming Unit Tests Acceptance Tests Daily meetings Iterations Releases Agile insists on constant feedback in all levels Empirical Feedback
- 3. Acceptance test driven development Write a failing acceptance test Write a failing unit test Make the test pass Refactor Regression Test suite Measure of demonstrable progress
- 4. •Start with Testing a walking skeleton •A “walking skeleton” is an implementation of the thinnest possible slice of real functionality that we can automatically build, deploy, and test end-to-end. Eg., for a database-backed web application, a skeleton would show a flat web page with fields from the database •The “end” in “end-to-end” refers to the process, as well as the system How to startTDD?
- 5. How do we write a test ? Write Tests Backwards •Write the test name - helps us decide what we want to achieve; •Write the call to the target code - is the entry point for the feature; •Write the expectations and assertions - know what effects the feature should have; •Write the setup and teardown to define the context for the test This sequence reflects how we tend to think through a new unit test. Then we run it and watch it fail.
- 6. Object Oriented Programming A Train Wreck (This is bad because this one line depends on the interfaces and implied structure of three different objects.) dog.getBody().getTail().wag(); Solution: "Tell, Don't Ask” dog.expressHappiness(); An object should only talk to its neighbors
- 7. Role of Mockobjects TDD with Mock Objects guides interface design by the services that an object requires, not just those it provides. System of narrow interfaces each of which defines a role in an interaction between objects, rather than wide interfaces that describe all the features provided by a class. LEAN
- 8. Format of TDD using Mockobjects Create instances of Mock Objects Set state in the Mock Objects Set expectations in the Mock Objects Invoke domain code with Mock Objects as parameters Verify consistency in the Mock Objects
- 9. TDD for distributed teams "Collective Code Ownership" is critical to distributed agile teams Continuous Integration should accommodate infrastructure for TDD You can’t go home with anything that doesn’t build !!