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ISTQB Advanced CTAL Exam-Study Guide-Part 5

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ISTQB Advanced CTAL Exam-Study Guide-Part 5

Prior to appearing for exam for ISTQB Advanced Level certification, it is wise to quickly brush up your knowledge by reviewing the following questions Ė answers that are extremely important from the examination point of view.

Q. 41: What is Conditional testing?

In conditional testing, each clause in every condition is forced to take on each of its possible values in combination with those of other clauses. Conditional testing thus subsumes branch testing. Instrumentation for conditional testing can be accomplished by breaking compound conditional statements into simple conditions and nesting the resulting if statements. This reduces the problem of conditional coverage to the simpler problem of branch coverage, enabling algorithms from the control flow view to be employed.

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Q. 42: What is Expression testing?

Expression testing requires that every expression assume a variety of values during a test in such a way that no expression can be replaced by a simpler expression. Expression testing requires significant runtime support for the instrumentation.

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Q. 43: What is Domain testing?

The input domain of a program can be partitioned according to which inputs cause each path to be executed. These partitions are called path domains. Faults that cause an input to be associated with the wrong path domain are called domain faults. Other faults are called computation faults. The goal of domain testing is to discover domain faults by ensuring that test data limit the range of undetected faults. This is accomplished by selecting inputs close to boundaries of the path domain. If the boundary is incorrect, these points increase the chance of an infectionís occurring. Domain testing assumes coincidental correctness does not occur, i.e., it assumes a program will fail if an input follows the wrong path.

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Q. 44: What is Perturbation testing?

Perturbation testing attempts to determine a sufficient set of paths to test for various faults in the code. Faults are modeled as a vector space, and characterization theorems describe when sufficient paths have been tested to discover both computation and domain errors. Additional paths need not be tested if they can not reduce the dimensionality of the error space.

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Q. 45: What is Fault sensitivity testing?

Foster describes a method for selecting test data that are sensitive to faults. Howden has formalized this approach in a method called weak mutation testing. Rules for recognizing fault-sensitive data are described for each primitive language construct. Satisfaction of a rule for a given construct during testing means that all alternate forms of that construct have been distinguished. This has an obvious advantage over mutation testing - elimination of all mutants without generating a single one! Some rules even allow for infinitely many mutants.

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Q. 46: What is Propagation oriented testing?

A testing technique is considered propagation oriented if it seeks to ensure that potential infections propagate to failures. This requires selecting paths to test based on their propagation characteristics.

Following are the types of propagation oriented testing:

1) Path testing
2) Compiler-based testing
3) Data flow testing
4) Mutation testing

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Q. 47: What is Path testing?

In path testing, data are selected to ensure that all paths of the program have been executed. In practice, of course, such coverage is impossible to achieve, for a variety of reasons. First, any program with an indefinite loop contains infinitely many paths, one for each iteration of the loop. Thus, no finite set of data will execute all paths. The second difficulty is the infeasible path problem: it is undecidable whether an arbitrary path in an arbitrary program is executable. Attempting to generate data for such infeasible paths is futile, but it cannot be avoided. Third, it is undecidable whether an arbitrary program will halt for an arbitrary input. It is therefore impossible to decide whether a path is finite for a given input.

In response to these difficulties, several simplifying approaches have been proposed. Infinitely many paths can be partitioned into a finite set of equivalence classes based on characteristics of the loops. Boundary and interior testing requires executing loops zero times, one time, and, if possible, the maximum number of times. Linear sequence code and jump criteria specify a hierarchy of successively more complex path coverages.

Path coverage does not imply condition coverage or expression coverage, since an expression may appear on multiple paths but some subexpressions may never assume more than one value.

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Q. 48: What is Compiler-based testing?

In a compiler based testing input-output pairs are encoded as a comment in a procedure, as a partial specification of the function to be computed by that procedure. The procedure is then executed for each of the input values and checked for the output values. The test is considered adequate only if each computational or logical expression in the procedure is determined by the test; i.e., no expression can be replaced by a simpler expression and still pass the test.

Simpler is defined in a way that allows only finitely many substitutions. Thus, as the procedure is executed, each possible substitution is evaluated on the data state presented to the expression. Those that do not evaluate the same as the original expression are rejected. Substitutions that evaluate the same, but ultimately produce failures, are likewise rejected.

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Q. 49: What is Data Flow Testing?

Data flow analysis can form the basis for testing exploiting the relationship between points where variables are defined and points where they are used. By insisting on the coverage of various definition-use pairs, data flow testing establishes some of the conditions necessary for infection and partial propagation. The motivation behind data flow testing is that test data are inadequate if they do not exercise these various definitions use combinations. It is clear that an incorrect definition that is never used during a test will not be caught by that test. Similarly, if a given location incorrectly uses a particular definition, but that combination is never tried during a test, the fault will not be detected.

Data flow connections may be determined statically or dynamically. Some connections may be infeasible due to the presence of infeasible subpaths. Heuristics may be developed for generating test data based on data flow information.

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Q. 50: What is Mutation testing?

Mutation testing uses mutation analysis to judge the adequacy of test data. The test data are judged adequate only if each mutant is either functionally equivalent to the original program or computes output different from the original program on the test data. Inadequacy of the test data implies that certain faults can be introduced into the code and go undetected by the test data.

Mutation testing is based on two hypotheses. The competent programmer hypothesis says that a competent programmer will write code that is close to being correct; the correct program, if not the current one, can be produced by some straightforward syntactic changes to the code. The coupling effect hypothesis says that test data that reveal simple faults will uncover complex faults. Thus, only single mutants need be eliminated, and combinatoric effects of multiple mutants need not be considered. Gourlay characterizes the competent programmer hypothesis as a function of the probability of the test setís being reliable and shows that under this characterization, the hypothesis does not hold. Empirical justification of the coupling effect has been attempted, but theoretical analysis has shown that it may hold probabilistically, but not universally.

Reference: Technical archive from SEI - Software Engineering Institute

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