Integration Testing & Its Strategies
Integration testing is a logical extension of unit testing. Integration testing identifies problems that occur when units are combined. It is the first level of testing which formally integrates a set of programs that communicate among themselves via messages or files (a client and its server(s), a string of batch programs, or a set of online modules within a dialog or conversation.)
You can do integration testing in a variety of ways but the following are three common strategies:
The top-down approach to integration testing requires the highest-level modules be test and integrated first. This allows high-level logic and data flow to be tested early in the process and it tends to minimize the need for drivers. However, the need for stubs complicates test management and low-level utilities are tested relatively late in the development cycle. Another disadvantage of top-down integration testing is its poor support for early release of limited functionality.
The bottom-up approach requires the lowest-level units be tested and integrated first. These units are frequently referred to as utility modules. By using this approach, utility modules are tested early in the development process and the need for stubs is minimized. The downside, however, is that the need for drivers complicates test management and high-level logic and data flow are tested late. Like the top-down approach, the bottom-up approach also provides poor support for early release of limited functionality.
The third approach, sometimes referred to as the umbrella approach, requires testing along functional data and control-flow paths. First, the inputs for functions are integrated in the bottom-up pattern discussed above. The outputs for each function are then integrated in the top-down manner. The primary advantage of this approach is the degree of support for early release of limited functionality. It also helps minimize the need for stubs and drivers. The potential weaknesses of this approach are significant, however, in that it can be less systematic than the other two approaches, leading to the need for more regression testing.
[Source]
Also See:
Big-Bang Testing
Disadvantages of Big-Bang Testing
Acceptance Testing
Difference between Acceptance & System Testing
System Testing
Examples of Integration & System Testing
Difference between Integration & System Testing
Integration Test Plan Template
Integration & System Testing Checklist