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Analysis and Design
Unit testing ensures that all modules have been tested and each of them works
properly individually. Unit testing does not guarantee if these modules will work
fine if these are integrated together as a whole system. It is observed that many
errors crop up when the modules are joined together. Integration testing uncovers
errors that arises when modules are integrated to build the overall system.
Following types of errors may arise:
Data can be lost across an interface. That is data coming out of a module is
not going into the desired module.
Sub-functions, when combined, may not produce the desired major function.
Individually acceptable imprecision may be magnified to unacceptable levels.
For example, in a module there is error-precision taken as +- 10 units. In other
module same error-precision is used. Now these modules are combined. Suppose the
errorprecision from both modules needs to be multiplied then the error precision
would be +-100 which would not be acceptable to the system.
Global data structures can present problems: For example, in a system there
is a global memory. Now these modules are combined. All are accessing the same
global memory. Because so many functions are accessing that memory, low memory
problem can arise.
Integration testing is a systematic technique for constructing the program
structure while conducting tests to uncover errors associated with interfacing.
The objective is to take unit tested modules, integrate them, find errors, remove
them and build the overall program structure as specified by design.
There are two approaches in integration testing. One is top down integration
and the other is bottom up integration. Now we'll discuss these approaches.
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