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What's the difference between "top-down" and "bottom-up" approach?

Integration testing has 2 approaches:

  1. Big bang approach – In this approach all modules are integrated all at once and then testing is done.
  2. Incremental approach – In this approach, logically related modules are joined. As the process of testing continues more such related modules are added and testing is continued till all modules are tested. Stubs and drivers are used in this process.

Incremental approach is divided into 2 categories:

  1. Top down Approach: In this approach testing process is carried out from top to bottom following the control flow of the system. Main module is divided into sub modules. Stubs are used in this approach. The module which is tested will call the stub. Stub is a dummy module which is created if the sub module is not created and it is used to simulate communication with the calling module.



  1. Fault localization is easy.
  2. High priority modules are tested first.
  3. Major design faults can be detected and fixed.
  1. Lots of stubs have to be created.
  1. Bottom Up Approach: In this approach the testing process is carried out from bottom to up, i.e., the lower level functionalities or modules will be tested first working its way up to the higher level functionalities.



  1. Fault localization is easier.
  2. In this approach no time is wasted in waiting for all modules to build like big bang approach.
  1. Critical modules are tested in the end so they may contain errors.

The winner! Well, there is a tie in this case because both have their own shares of pros and cons. So it is you who should decide which approach you wish to follow depending on your convenience and requirement.

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