What is Test Driven Development - Learn the Methods & Tools

What is Test Driven Development - Learn the Methods & Tools

by Inflectra on

What is Test Driven Development?

Test-Driven Development (TDD) originally was created as part of the Extreme Programming (XP) methodology, where it was known as ‘Test-First’ concept. The idea is that developers generally write their tests after the code is written and therefore are only testing the functionality as they wrote it, as opposed to testing it to make sure it works the way it was actually intended!

Also there is a tendency when writing a test after the fact of only writing the code to test the so-called ‘happy path’ – the path that the developer expects the user to take. The usual process follows these steps:

The requirements are defined, from these requirements, the development team creates the design of a specific part of the application, and the developers then write the necessary production code. They will then document the code after the fact and create tests (manual and/or automated) to test that the system works as expected. The testers then run the tests, and any bugs found are then fixed.

This approach means that (a) you are only testing the system based on the code that was already written, and (b) when you change the system to fix one of the identified bugs, there is not an automated way to make sure you have not changed the design or introduced new bugs.

With a test-driven-development approach, the process is somewhat different:

The requirements are used to directly create the acceptance tests (the ones that determine if the system meets the needs of the users / stakeholders as defined by the requirements). The team uses the requirements and acceptance tests to design the system and create the appropriate unit tests. These tests are now executed, and (since nothing yet exists) will naturally fail. However the unit tests are now the detailed definition of the requirements.

The team then writes the production code so that the tests now pass. The new code written at this stage is not perfect, and may, for example, pass the test in an inelegant way. That is acceptable because later steps improve and hone it. At this point, the only purpose of the written code is to pass the test; no further (and therefore untested) functionality should be predicted and 'allowed for' at any stage.

Now the code should be cleaned up as necessary. Move code from where it was convenient for passing the test to where it logically belongs. Remove any duplication you can find. Make sure that variable and method names represent their current use. Clarify any constructs that might be misinterpreted. By re-running the test cases, the developer can be confident that code refactoring is not damaging any existing functionality. This refactoring process is a key attribute of agile development methods such as XP and Scrum.

One final aspect is that whenever a bug is found, that implies that the unit test coverage of the system is not sufficient, and before fixing the bug, the unit tests should be extended to reproduce the bug as a test failure. Only once this has been done, should the bug be fixed (causing the new test to pass). This ensures that any old bugs are not inadvertently reopened in the future.

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SpiraTeam Extreme Programming Scrum DSDM
Summary Requirement Epic Epic Feature Group
Requirement User Story Backlog Item Requirement
Task Task Task Task
Release Release Release Release
Iteration Iteration Sprint Iteration
Test Case Acceptance Test Acceptance Test Test

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