Integration testing

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Integration testing techniques
1)Top-Down Integration
2)Bottom-up Integration
3)Big-bang Integration

Top down Integration Test
1)program and tested from the top to the bottom
2)The modules are integrated by moving downward through the control hierarchy, beginning with the main control module Ref. fig 1
3)The modules subordinate to the main control module are incorporated into the structure in either a depth or breadth first way first.

Advantages
Integrated Testing is done in an environment that closely resembles that of reality, so the tested product is more reliable
Stubs are functionally simpler than drivers, and therefore can be written with less time and labor

Disadvantages
Basic functionality test at the end of cycle 

Bottom Up Integration

Start building and testing with atomic modules (ie modules of the lowest levels in the structure of the program.
Fuses and tested program from the bottom upwards.
The terminal module is tested in isolation first, then the next set of higher level modules are tested with the lower pre-tested modules.

Advantages
Programming and testing operations can be performed simultaneously, obtaining noticeable improvements in the efficiency of software development
Unit Testing of each module can do very well

Disadvantages
Key interface defects trapped at the end of cycle
Test drivers have to be generated for modules at all levels except the top control
We can test the program in the real environment in which to run.

Big Bang Tests

One type of integration testing in which software components are combined in one application at a time on a global system.Under this approach, each unit module is first tested in isolation of each module. After each module is tested, all modules are integrated together at once..