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Top Down Approach


What is Top down approach?

At the time of software testing using the integration technique, the functionality of the software being tested, is divided into independent modules. Top down is that approach which employs testing starting from the highest or main module and proceeds downwards to the lower or sub modules.

Performing top down integration testing with an example

One of the chief features of top down approach is the use of under developed temporary modules called STUBS. If we suppose a software functionality needs to be tested with one main module A in combination with two to three sub modules (numbered 2&3), then we say that the testing will start from the module A and will proceed step by step towards testing of communication between sub modules 2 and 3. In addition to this we simulate the behaviour of another combination of sub modules called stubs which have been developed for testing at a level lower than sub modules 2 and 3. Likewise we proceed further down to testing of sub modules present lower down the pecking order.

Advantages of top down approach

  • Since the main module is tested first, the chief functionalities are tested on a priority basis.
  • Creation and the use of stubs have an edge over the use of drivers when faced with time constraints.
  • Since the product is tested in an environment pretty similar to the one encountered in a real world scenario, the tested product is a lot more consistent.
  • At the time of testing, the top down approach allows us to create a temporarily working framework for showing to the clients or management on a short notice.

Demerits of top down approach

  • Development of stub modules can be quite a tedious process.
  • Before the input or output functions are added, fitting of stub modules can be difficult.
  • Test conditions are relatively difficult to create with this approach.
  • There is likelihood of simple functionalities being tested at the last stages.

Conclusion

To conclude we can say that testing using top down approach allows us to create a sturdy and uniform framework for the software product being tested before its eventual release.