What is Bottom-Up Integration testing?

Bottom-Up Integration testing is a kind of testing methodology in which the modules are tested from the bottom of control flow upwards. Bottom-Up integration testing is opposite to the Top-down integration testing. In this testing first the bottom modules of lower levels are tested and then the higher level modules are tested.

bottom up integration testing diagram

The above given figure shows the bottom-up testing hierarchy. The above given figure shows that each component at the lower hierarchy is tested first and then the upper level components are tested. From the above given figure the order of integration will be shown as follows:
4, 2
5, 2
6, 3
7, 3
2, 1
3, 1

First all the lower level components such as 4,5,6,7 are tested and then the components above them such as 2 and 3 which calls 4, 5 and 6, 7 respectively. Then at last the higher level component 1 is tested.




Advantages of Bottom-up integration testing:

  • Development and testing phases can be started together.
  • As the lower level components are tested first, means all the complex modules are tested first. So any error in the complex modules will be solved in the early stage only.

Disadvantages of Bottom-up testing:

  • The organizational phase have to be changed in the latter phase if needed.
  • No working model can be presented in the early stages.
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