This model derives its name from the way in which the software is built. More specifically, the model is designed, implemented and tested as a series of incremental builds until the product is finished. A build consists of pieces of code from various modules that interact together to provide a specific function. At each stage of the IM a new build is coded and then integrated into the structure, which is tested as a whole. Note that the product is only defined as finished when it satisfies all of its requirements.

“A clever person solves a problem. A wise person avoids it. – Einstein”

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Testing without knowledge of the internal workings of the item being tested. 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

The advantages of this type of testing include:

1. The test is unbiased because the designer and the tester are independent of each other.
2. The tester does not need knowledge of any specific programming languages.
3. The test is done from the point of view of the user, not the designer.
4. Test cases can be designed as soon as the specifications are complete.


The disadvantages of this type of testing include:

1. The test can be redundant if the software designer has already run a test case.
2. The test cases are difficult to design.
3. Testing every possible input stream is unrealistic because it would take a inordinate amount of time; therefore, many program paths will go untested.



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White Box testing is done with the code perspective. The emphasis is to ensure that each line of the code is executed atleast once.

Unit Testing: Testing performed to isolate and expose faults and failures as soon as the source code is available, regardless of the external interfaces that may be required. Often times, the detailed design and requirements documents are used as a basis to compare how and what the unit is able to perform. White and black-box testing methods are combined during unit testing.

Can derive test cases to ensure:

1. all independent paths are exercised at least once.
2. all logical decisions are exercised for both true and false paths.
3. all loops are executed at their boundaries and within operational bounds.
4. all internal data structures are exercised to ensure validity.


Why White box testing when black box testing is there to test conformance to requirements
- Logic errors and incorrect assumptions most likely to be made when coding for "special cases". Need to ensure these execution paths are tested.
- May find assumptions about execution paths incorrect, and so make design errors. White box testing can find these errors.
- Typographical errors are random. Just as likely to be on an obscure logical path as on a mainstream path.

"Bugs lurk in corners and congregate at boundaries"

White Box Testing Techniques

1. Basis Path Testing
a. Flow Graph Notation
b. Cyclomatic Complexity
c. Deriving Test Cases
d. Graph Matrices
2. Control Structure testing
a. Conditions Testing
b. Data Flow Testing
c. Loop Testing



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Test designed based on the knowledge of algorithm, internal states, architectures, or other high -level descriptions of the program behavior.

Gray box testing combines white box techniques with black box input testing. Gray box approaches usually require using several tools together. A good example of a simple gray box analysis is running a target program within a debugger and then supplying particular sets of inputs to the program. In this way, the program is exercised while the debugger is used to detect any failures or faulty behavior. Rational's Purify is a commercial tool that can provide detailed runtime analysis focused on memory use and consumption. This is particularly important for C and C++ programs (in which memory problems are rampant).


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