I've read lots of articles on the internet but still having confusion, what really happens in both of them and what is the difference between them ?

Could someone please elaborate with a real time example by taking a Web/mobile application ?

3 Answers 3


In a nutshell,

  • Big bang testing involves real software components after each component has been finished; all of the components have never been tested before.
  • Top down testing involves lower level stubs software components. Low as in abstract level, the more abstract a software concept / component is the higher level it has.

An example,

  • You are building a mobile Online Multiple Player game.
  • Big bang testing happens when all developers put their work together and see if it works. By their work, I mean functional components such as interactive buttons, animations, damaging / healing algorithm, network searching algorithm and etc. Those components have never been put together before, e.g. they have been under development in isolation, out of sudden, they are put together, therefore a big bang.
  • Top down testing happens when low level stubs are introduced. E.g. when the attacking animation has not been finished, but developers need to know if the attacking algorithm is working properly; they may build a simple method that mimic the intended behaviors of the attacking animation for testing purpose.

In Bigbang Approach, the entire project or system is completed, and the testing is done on the entire system.

In Top Down approach, the developers develop higher level components first. To test these components in higher hierarchy, we need stubs or programs which simulate action of lower order hierarchy components.

The stubs are used so that the testers do not have to wait for the lower components to be developed in order to be test the higher components thoroughly.


In a software testing company both the approach/strategies are executed to perform integration testing for an application:

Just consider a simple dummy application that has set of 5 modules say Module1--->Home page of RI application Module2-->Login page Module3-->Existing user page after successful login Module4->Log out Module5->page for invalid login attempt

In Top Down approach: Integration testing starts with the higher level module and goes to its next level.If at any stage it is found that some mandatory module is missing, then in such an event that particular module is replaced with a temporary program known as "Stub".

For the above mentioned case,The testing starts with M1. To test M1 in isolation, communications to modules M2, M3 and M4 needs to be simulated by the tester by some means, since these modules may not be ready yet.

In Big Bang Approach: In this approach, integration testing starts once all the modules are ready after testing individually.

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