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A software undergoes many levels of testing from unit testing to integration to system testing. As information system are becoming more complex, object oriented paradigm is gaining popularity because of its benefits in analysis, design and coding. Conventional testing cannot be applied for testing classes because of problems involved in testing class, abstract classes, inheritance, dynamic binding, message passing, polymorphism etc. Object oriented testing methods are similar to those of conventional testing methods. Three or four levels of object oriented testing are used, depending on the choice of what constitutes a unit. If individual functions are chosen as units, we have four levels of testing namely: Operation testing: It is testing of individual function i.e. the function works according to the requirement. Like for instance an 'addition' function does addition of two numbers and no other mathematical operation. Class testing: It is testing of interaction among previously testing methods/operations. Like, the above tested 'addition' function works intact even after introduction of a 'subtraction' function in the class. Interclass testing: It is a major part of out and is concerned with testing interaction among previously tested classes. Like, a class which has the mathematical operation functions when integrated with a class that contains operation for calculations of areas of various shapes, performs its mathematical operations correctly. System testing: It is conducted at port level entry and is concerned with testing of the entire system as a whole before being delivered to the customer. Of the three main levels of software testing interclass testing is the least understood both in object oriented and traditional testing terms. Interclass testing is referred as Integration testing in general terms.