Black Box Testing Also known as specification-based testing Tester has access only to running code and the specification it is supposed to satisfy Test cases are written with no knowledge of internal workings of the code No access to source code So test cases don’t worry about structure Emphasis is only on ensuring that the contract is met Black-box testing attempts to find errors in the following categories: Incorrect or missing functions Interface errors Errors in data structures or external database access Behavior or performance errors Initialization and termination errors. Advantages Scalable; not dependent on size of code Testing needs no knowledge of implementation Tester and developer can be truly independent of each other Tests are done with requirements in mind Does not excuse inconsistencies in the specifications Test cases can be developed in parallel with code Disadvantages Test size will have to be small Specifications must be clear, concise, and correct May leave many program paths untested Weighting of program paths is not possible Test Case Design Examine pre-condition, and identify equivalence classes All possible inputs such that all classes are covered Apply the specification to input to write down expected output Equivalence Partitioning Input data for a program unit usually falls into a number of partitions, e.g. all negative integers, zero, all positive numbers Each partition of input data makes the program behave in a similar way Two test cases based on members from the same partition is likely to reveal the same bugs By identifying and testing one member of each partition we gain 'good' coverage with 'small' number of test cases Testing one member of a partition should be as good as testing any member of the partition Example: for binary search the following partitions exist Inputs that conform to pre-conditions Inputs where the precondition is false Inputs where the key element is a member of the array Inputs where the key element is not a member of the array Pick specific conditions of the array The array has a single value Array length is even Array length is odd Boundary Value Analysis Arises from the fact that most program fail at input boundaries Suppose system asks for “a number between 100 and 999 inclusive” The boundaries are 100 and 999 We therefore test for values 99 100 101 Lower Boundary 999 999 1000 Upper Boundary
