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Tuesday, August 12, 2014

Test Driven Development - The Process

Continuing from the previous post on the basics of TDD (link), this post continues with the topic of Test Driven Development.

What is the process of Test Driven development?
For the test driven development to be implemented on some software artifact, its units should be kept small. By units here we mean a group or class of functions related to each other. Sometimes these units might also be referred to as the modules. These are a couple of the benefits of using small units:
> The debugging effort is reduced – Upon detection of test failures; it becomes easy to track down the faults when you have smaller units.
> Tests are often self – documenting: Readability and understandability is increased by virtue of small tests.

TDD can be converted into ATDD (acceptance test driven development) by mixing TDD with more advanced practices. The criteria that the customer specifies are converted into acceptance tests which are then used for driving the UTDD (unit TDD) process in traditional manner. With this process it is ensured that there is an automated mechanism which can be used by the customers for deciding whether their requirements have been met or not. The ATDD provides the development team with a fixed target i.e., the acceptance tests which keeps them steadily focused on the requirements of the customers. Now let us examine the TDD cycle. It's test driven development cycle consists of the following phases:

1. Adding a test: The beginning of a new feature is marked by writing a test which must fail because of being written before the implementation of the feature. If this test succeeds then either the test is defective or the feature has already been added to the software. Before writing a test, the requirements and specifications must be fully understood by the developer by means of user stories and use case stories. This step puts the focus of the developer on the requirements before he/ she begins writing the code that makes a subtle yet importance difference.
2. Running the tests and checking if they fail: This step does the step of validating the correct working of the test harness. The test itself is also tested in this process ruling out the possibility that the new test will pass always. This results in increase in confidence in software.
3. Allowing the test to pass by writing some code: the code written at this step is not perfect as proved by later tests but it is eventually improved. The code is written only to pass the test.
4. Running the tests: If all the tests pass, the programmer can be sure of the code that the requirements are being met.
5. Refactoring the code: Now the code has to be refactored as required. This also involves placing the code in its logical place and removing any redundant code. It has to be made sure that the function and variable names represent properly their current values. Any misinterpreted constructs should be clarified. After this the code should be re – run to be sure that the refactored code has not changed the other functionalities.
6. Repeat: Another test is taken to test the next functionality. The steps should be kept small. If the new code does not satisfy this test or if it fails, the changes made should be undone instead of excessive debugging. Maintaining revertible checkpoints becomes easy if continuous integration is used. If external libraries are being used, then it is necessary that the size of the increments should be as small as the library itself unless the library is not sufficient or it has bugs. Between each test run, there can be maximum 10 edits. This cycle goes on until all the functionalities have been tested.

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