Integration testing's purpose is to ensure that each as-built component behaves according to its specification defined during preliminary design. Unit Test Planning generates and documents plans and procedures to test each module independently and thoroughly. Integration Test Planning generates and documents plans and procedures to effect an orderly system integration. System Test Planning development and documentation of test plans and procedures. Objectives Testing cannot show the absence of defects, it can only show that software defects are present.
Testing is a process of executing a program with the intent of finding an error.
A good test case is one that has a high probability of finding an as yet undiscovered error. A successful test is one that uncovers an as yet undiscovered error. With large systems, it is almost always true that more testing will find more defects. The question is not whether all the defects have been found, but whether the cost of discovering the remaining defects can be justified. Hence, strategies for testing should be adopted that optimize the effort expended.