Quality is delighting customers
Testing takes place from top to bottom. High-level modules are tested first and then low-level modules and finally integrating the low-level modules to a high level to ensure the system is working as intended.
In Software Testing,Top-down and bottom-up are both strategies of information processing and knowledge ordering, used in a variety of fields including software, humanistic and scientific theories, and management and organization. In
As per practices of top software testing companies, Top-down testing is also known as information processing and knowledge ordering and used in a variety of fields including software, scientific theories, management, and organization.
Top-Down integration testing is an incremental technique of building a program structure. The main purpose of top-down integration is to verify the significant control and decision points earlier in the test process.
This testing has been done from the main module to submodule. If the submodule is not developed yet then a temporary program called STUB is used to simulating the submodule.
There are three modules Module 1, Module 2 and Module 3 and there are some sub-modules like Stub 1, Stub 2, Stub 3 and Stub 4.
Module 1, Module 2 and Module 3 are available for integrations, whereas Stub 1, Stub 2, Stub 3 and Stub 4 are still under development that cannot be integrated at this point of time. Hence, Stubs are used to test the modules.
So in above testing approach is like as:
The team will test the integration between modules 1, 2 and 3.
The team will test the integration between module 2 and stub 1, stub 2.
In the last team will test the integration between the module 3 and stub 3, stub 4.
And when Stub 1, Stub 2, Stub 3 and Stub 4 are gets developed they will become independent modules then the team will do top-down integration testing between Modules 1, 2, 3, Module 4(before development stub1), Module 5, Module 6, Module 7.
In this testing critical Modules are tested on priority; major design flaws could be found and fixed first.
Team Test conditions are easier to create.
Observation of test results is easier.
The program as an entity does not exist until the last module is added.
Modules at a lower level are tested inadequately.