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Black Box Vs White Box Testing

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Black Box Testing also known as Behavioral testing is a software testing technique whereby the internal workings of the item being tested are not known by the tester.

For example, when black box testing is applied to software engineering, the tester would only know the "legal" inputs and what the expected outputs should be, but not how the program actually arrives at those outputs. It is because of this that black box testing can be considered testing with respect to the specifications, no other knowledge of the program is necessary

For example, in a black box test on software design the tester only knows the inputs and what the expected outcomes should be and not how the program arrives at those outputs. The tester does not ever examine the programming code and does not need any further knowledge of the program other than its specifications.

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.

The advantages of this type of Testing include:

  • The test is unbiased because the designer and the tester are independent of each other.
  • The tester does not need knowledge of any specific programming languages.
  • The test is done from the point of view of the user, not the designer.
  • Test cases can be designed as soon as the specifications are complete.
  • More effective on larger units of code than glass box testing
  • Tester needs no knowledge of implementation, including specific programming languages
  • Tester and programmer are independent of each other
  • Tests are done from a user's point of view
  • Will help to expose any ambiguities or inconsistencies in the specifications
  • Test cases can be designed as soon as the specifications are complete

The disadvantages of this type of testing include:

  • The test can be redundant if the software designer has already run a test case.
  • The test cases are difficult to design.
  • Testing every possible input stream is unrealistic because it would take a inordinate amount of time; therefore, many program paths will go untested.
  • Only a small number of possible inputs can actually be tested, to test every possible input stream would take nearly forever
  • Without clear and concise specifications, test cases are hard to design
  • There may be unnecessary repetition of test inputs if the tester is not informed of test cases the programmer has already tried
  • May leave many program paths untested
  • Cannot be directed toward specific segments of code which may be very complex (and therefore more error prone)
  • Most testing related research has been directed toward glass box testing

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