Testing of a function with knowing internal structure of the program.
White box testing involves looking at the structure of the code. When you know the internal structure of a product, tests can be conducted to ensure that the internal operations performed according to the specification. And all internal components have been adequately exercised. In other word WBT tends to involve the coverage of the specification in the code.
Code coverage is defined in six types as listed below.
• Segment coverage – Each segment of code b/w control structure is executed at least once.
• Branch Coverage or Node Testing – Each branch in the code is taken in each possible direction at least once.
• Compound Condition Coverage – When there are multiple conditions, you must test not only each direction but also each possible combinations of conditions, which is usually done by using a ‘Truth Table’
• Basis Path Testing – Each independent path through the code is taken in a pre-determined order. This point will further be discussed in other section.
• Data Flow Testing (DFT) – In this approach you track the specific variables through each possible calculation, thus defining the set of intermediate paths through the code i.e., those based on each piece of code chosen to be tracked. Even though the paths are considered independent, dependencies across multiple paths are not really tested for by this approach. DFT tends to reflect dependencies but it is mainly through sequences of data manipulation. This approach tends to uncover bugs like variables used but not initialize, or declared but not used, and so on.
• Path Testing – Path testing is where all possible paths through the code are defined and covered. This testing is extremely laborious and time consuming.
• Loop Testing – In addition top above measures, there are testing strategies based on loop testing. These strategies relate to testing single loops, concatenated loops, and nested loops. Loops are fairly simple to test unless dependencies exist among the loop or b/w a loop and the code it contains.
In WBT, we use the control structure of the procedural design to derive test cases. Using WBT methods a tester can derive the test cases that
• Guarantee that all independent paths within a module have been exercised at least once.
• Exercise all logical decisions on their true and false values.
• Execute all loops at their boundaries and within their operational bounds
• Exercise internal data structures to ensure their validity.
White box testing (WBT) is also called Structural or Glass box testing.
We do WBT because Black box testing is unlikely to uncover numerous sorts of defects in the program. These defects can be of the following nature:
• Logic errors and incorrect assumptions are inversely proportional to the probability that a program path will be executed. Error tend to creep into our work when we design and implement functions, conditions or controls that are out of the program
• The logical flow of the program is sometimes counterintuitive, meaning that our unconscious assumptions about flow of control and data may lead to design errors that are uncovered only when path testing starts.
• Typographical errors are random, some of which will be uncovered by syntax checking mechanisms but others will go undetected until testing begins.
Talking theoretically, all we need to do in WBT is to define all logical paths, develop test cases to exercise them and evaluate results i.e. generate test cases to exercise the program logic exhaustively.
For this we need to know the program well i.e. We should know the specification and the code to be tested; related documents should be available too us .We must be able to tell the expected status of the program versus the actual status found at any point during the testing process.
