Berrached::CS3320::Ch131 Implementation Phase Chapter 13 Classical & Object-Oriented Software Engineering by Stephen R. Schach

Berrached::CS3320::Ch132 Implementation Phase Aim: to translate the detailed design into code. Programming-in-the-many: Product is implemented by a team of programmers All working at same time on different components of the product.

Berrached::CS3320::Ch133 Outline Choice of programming language Good Programming Languages Testing Techniques

Berrached::CS3320::Ch134 Choice of a Programming Language Language usually specified in contract by client. If not, choice should be based on: –cost-benefit analysis –COBOL: for data processing –Object-Oriented Languages –4th generation Languages: e.g. SQL, DB2, Oracle, PowerBuilder Higher-level: each line equivalent to line of machine code ease in programming, but slower mostly for data processing tasks

Berrached::CS3320::Ch135 Good Programming Practice Use of consistent and meaningful variable name –Meaningful to future maintenance programmer –Consistent to aid maintenance programmer Example: –Module contains a variable to represent maximum, minimum, and average temperatures: MaxFr: too ambiguous frequencyMax, minFreq: not consistent maxFrequency, minFreqency, avgFrequency –Companies usually have their own internal conventions.

Berrached::CS3320::Ch136 Good Programming Practice CNTD Self-documenting code: code can be understood without the aid of comments: –very rare Key question: –Can module be understood easily and unambiguously by SQA team maintenance programmers all others who have to read code –E.g. xCooddinateOfPositionOfRobotArm abbreviate to xCoord

Berrached::CS3320::Ch137 Prologue Comments Mandatory at top of every single module –module name –brief description of what module does –programmer’s name –date module was coded –date it was approved and by whom –Module parameters –Variable name, alphabetically and their uses –files accessed and updated by module –module I/O –error handling capabilities –name of file of test data –list if modifications made, when, by whom, approved by whom –known faults, if any

Berrached::CS3320::Ch138 Other Comments In-line comments needed to explain code Fallacy: –Comment are only needed when code is written in non- obvious way, or makes use of subtle aspect of language –If that is the case, re-code in clearer way Code layout for increased readability –use indentation –use blank lines

Berrached::CS3320::Ch139 Nested if Statements

Berrached::CS3320::Ch1310 Nested if Statements CNTD

Berrached::CS3320::Ch1311 Nested if Statements CNTD

Berrached::CS3320::Ch1312 Nested if Statements CNTD

Berrached::CS3320::Ch1313 Nested if Statements CNTD Combination of if-if and if-else-if statements usually difficult to read simplify by making use of fact that if-if combination if is frequently equivalent to single condition if && Note: if programming language supports “short-circuit” evaluation of logical operations, they can always be equivalent.

Berrached::CS3320::Ch1314 Nested if Statements CNTD Some basic rules: –if conditions are interdependent, use if-else statement instead of a sequence of if statements –Don’t forget the final else part –Avoid if-if and if-else-if statements by combining conditions using the && operator –Rule of thumb: if-statements nested to depth greater than three should be avoided as poor programming practice

Berrached::CS3320::Ch1315 Programming Standards Standards are difficult to enforce Can be both blessing and curse –setting limits of module size Examples of good standards –documentation standards –program layout –naming standards –“ nesting of if-statements should not exceed a depth of 3, except with prior approval from team leader” –“Use of goto should be avoided. However, with prior approval from team leader, a forward goto many be used for error handling”

Berrached::CS3320::Ch1316 Module Testing After preliminary testing by programmer, each module is handed over to SQA group for formal testing. How to methodically test a module?

Berrached::CS3320::Ch1317 Module Test Case Selection Worst way- random testing Need systematic way to construct test cases Two extremes to testing: 1. Test to specifications (also called black-box, data driven, functional, or input/output driven testing). Ignore code. Use spec. document to select test cases 2. Test to code (also called glass-box, logic-driven, structured, or path-oriented testing) Ignore specifications. Use code to select test cases

Berrached::CS3320::Ch1318 Feasibility Of Testing To Specs Example: –Specification for a data processing product include 5 commissions and 7 types of discount –35 test cases Suppose specs include 20 factors, each taking 4 values –4 20 or over 1 trillion test cases –if each takes 30 seconds to run, running all test cases takes > 1 million years!! Combinatorial explosion makes exhaustive testing to specification unfeasible.

Berrached::CS3320::Ch1319 Feasibility Of Testing To Code Each path through module must be executed at least once –Combinatorial explosion: flow chart has over different paths

Berrached::CS3320::Ch1320 Feasibility Of Testing To Code CNTD Can exercise every path without detecting every fault Example: if ( (x+y+z)/ 3 ==x) cout <<“x, y, z are equal”<<endl; else cout <<“x, y, z are not equal”<<endl; Test case 1: x=1, y=2, z=3 Test case 2: x=2, y=2, z=2

Berrached::CS3320::Ch1321 Feasibility Of Testing To Code CNTD Path can be tested only if it is present Example 1: if (d==0) zeroDivisionRoutine(); else x = n/d; Example 2: x = n/d;

Berrached::CS3320::Ch1322 Coping With The Combinatorial Explosion Exhaustive testing (to specs or to code) is not feasible Art of testing: Small, manageable set of test cases to –maximize chances of detecting faults, while –minimizing chances of wasting test cases Every test case must be designed to detect previously undetected faults Methods that will high-light as many faults as possible –First black-box test cases –Then glass-box methods

Berrached::CS3320::Ch1323 Black-Box Module Testing Equivalence Testing Example: –Specs for DBMS state that product must handle any number of records between 1 and 16,000 –if system works for any one test in range [1..16,000], then it will probably work for any test case in range range [1..16,00] constitutes one equivalence class Any one member is as good a test case as any other member of the class.

Berrached::CS3320::Ch1324 Equivalence Testing CNTD Range [1..16,000] defines three difference equivalence classes: –Equivalence Class 1: Fewer than 1 record –Equivalence Class 2: between 1 and 16,000 records –Equivalence Class 3: More than 16,000 records Boundary Analysis: –Selecting test case on or just to one side of boundary of equivalence class increases probability of detecting faults

Berrached::CS3320::Ch1325 Equivalence Testing & Boundary Analysis DBMS Example: –Test Case 1: 0 record: (member of class 1 & adjacent to boundary value) –Test Case 2: 1 record (Boundary value) –Test Case 3: 2 records (Adjacent to boundary value) –Test Case 4: 8349 records (member of class 2) –Test Case 5: 15,999 recs (Adjacent to Boundary value) –Test Case 6: 16,000 recs (Boundary value) –Test case 7: 16,001 recs (Adjacent to Boundary value)

Berrached::CS3320::Ch1326 Black-Box Testing Methods CNTD Functional Testing Test for each item of functionality Example: –module authenticates user login –Module computes some arithmetic function Weakness: –Functionality may span several modules

Berrached::CS3320::Ch1327 Glass-Box Module Testing Methods Statement Coverage Series of test cases to check every statement CASE tools needed to keep track Weakness: –Branch statements if (S > 1 && t = 0) // && should have been || X= 8; Test case: S=2, t=0 Both statements can be executed without fault showing up

Berrached::CS3320::Ch1328 Glass-Box Module Testing Methods Branch Coverage Series of tests check all branches. CASE tool needed Path Coverage Most powerful form of Glass box testing Weakness: with loops, number of paths very large, can be infinite Want weaker condition than all paths but which shows up more coverage than branch coverage

Berrached::CS3320::Ch1329 Glass-Box Module Testing Methods Path Coverage (continued) Linear code sequences: Identify set points L from which control flow may jump, including entry and exit points –e.g. Restrict test cases to paths that begin and end with elements of L Uncovers many faults without testing every path.

Berrached::CS3320::Ch1330 Glass-Box Testing Methods CNTD All-definition-use- path coverage Each occurrence of variable, zz say, is labeled either as –definition of variable: e.g. zz=1 or read(zz) –or use of variable: e.g. Y = zz + 1 or if (zz > 0) …. Identify all paths from definition of variable to use of that variable –can be done by automated tool Set up a test case for each such path.

Berrached::CS3320::Ch1331 Glass-Box Testing Methods CNTD All-definition-use- path coverage CNTD Disadvantages: –upper bound on number of paths is 2 d, where d is number of branches In practice –Actual number of paths is proportional to d

Berrached::CS3320::Ch1332 Glass-Box Testing Methods CNTD Infeasible Code May not be possible to test specific statement because there is an infeasible path ("dead code") if ( k < 2) { if ( k > 3) { // dead code …. Dead code is frequently an indication of a fault

Berrached::CS3320::Ch1333 Glass-Box Testing -- Quality Assurance Module m1 is more "complex" than module "m2" => m1 is likely to have more faults Software complexity –highlights modules most likely to have faults Unreasonably high complexity => re-design and re-code

Berrached::CS3320::Ch1334 Measures of Complexity Lines of code –simplest measure of complexity –underlying assumption: constant probability p that a line of code contains fault. Number of faults is related to size of product as a whole

Berrached::CS3320::Ch1335 Measures of Complexity Cyclomatic Complexity Essentially number of decisions (branches) in module Easy to compute Good measure of faults

Berrached::CS3320::Ch1336 Measures of Complexity Software Science Metrics Based on number of operators and operands in module Problem with cyclomatic and software science –Being challenged theoretically and experimentally –The both have high correlation wit LOC Several experiments have shown that LOC is as good predictor of fault rate as any other metrics Note: LOC is poor metric of productivity

Berrached::CS3320::Ch1337 Code Walkthrough and Inspections Done by SQA team –group of 4-6 members –"walkthrough" code –detect faults (no correction) Leads to rapid and thorough fault detection Experiments have shown that they are at least as effective in detecting faults as black-box and glass-box testing techniques.

Berrached::CS3320::Ch1338 CLEANROOM TESTING Incorporates several SW development techniques: –incremental process model –Formal techniques for specification and design –non-execution based testing: walkthroughs and inspections A module is not compiled until it has passed inspection

Berrached::CS3320::Ch1339 CLEANROOM TESTING 1820 lines of FoxBASE (U.S. Naval Underwater Systems Center, 1992) –18 faults detected by "functional verification" based correctness proving techniques –19 faults detected in walkthroughs before compilation –NO compilation errors –NO execution errors

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Berrached::CS3320::Ch1352 Approaches to Real Time Testing Non-execution based –Structure analysis techniques –deadlock detection methods –formal methods for modeling system behavior that can take synchronization into consideration –e.g. PetriNets

Berrached::CS3320::Ch1353 Approaches to Real Time Testing (CNTD) Execution Based –Systematic testing all possible ordering of inputs often impossible (combinatorial explosion) –Simulation is the most important testing method for real-time systems