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Comprehensive Guide to Debugging in Software Testing"
- 1. Software Debugging Dr. DurgaPrasad Mohapatra Professor National Institute of Technology Rourkela
- 2. Debugging Once errorsare identified: ◦ it is necessary to identify the precise location of the errors and to fix them. Each debugging approach has its own advantages and disadvantages: ◦ each is useful in appropriate circumstances.
- 3. Some Debugging Approaches •Brute Force method • Symbolic Debugger • Backtracking • Cause-Elimination Method • Program Slicing 3
- 4. Brute-force method Thisis the most common method of debugging: ◦ least efficient method. ◦ program is loaded with print statements ◦ print the intermediate values ◦ hope that some of printed values will help identify the error.
- 5. Symbolic Debugger Bruteforce approach becomes more systematic: ◦ with the use of a symbolic debugger, ◦ symbolic debuggers get their name for historical reasons ◦ early debuggers let you only see values from a program dump: determine which variable it corresponds to.
- 6. Symbolic Debugger Usinga symbolic debugger: ◦ values of different variables can be easily checked and modified ◦ single stepping to execute one instruction at a time ◦ break points and watch points can be set to test the values of variables.
- 7. Backtracking This isa fairly common approach. Beginning at the statement where an error symptom has been observed: ◦ source code is traced backwards until the error is discovered.
- 8. Example int main( ){ inti, j, s; i=1; while(i<=10){ s=s+i; i++; j=j++;} printf(“%d”,s); }
- 9. Backtracking Unfortunately, asthe number of source lines to be traced back increases, ◦ the number of potential backward paths increases ◦ becomes unmanageably large for complex programs.
- 10. Cause-elimination method Inthis method, once a failure is observed, the symptoms of the failure (e.g. certain variable is having a negative value though it should be positive) are noted. Determine a list of causes: ◦ which could possibly have contributed to the error symptom. ◦ tests are conducted to eliminate each. A related technique of identifying errors by examining error symptoms: ◦ software fault tree analysis.
- 11. Program Slicing Thistechnique is similar to back tracking. However, the search space is reduced by defining slices. A slice is defined for a particular variable at a particular statement: ◦ set of source lines preceding this statement which can influence the value of the variable.
- 12. Program Slicing cont… Slice of a program w.r.t. program point p and variable x: - All statements and predicates that might affect the value of x at point p. <p, x> known as slicing criterion.
- 13. Example 1 main( ) 2{ 3 int i, sum; 4 sum = 0; 5 i = 1; 6 while(i <= 10) 7 { 8 Sum = sum + 1; 9 ++ i; 10 } 11 printf(“%d”, sum); 12 printf(“%d”, i); 13 } An Example Program & its backward slice w.r.t. <12, i>
- 14. Program Dependence Graph 1 56 11 8 3 12 4 9 Control Dep Edge Data Dep Edge
- 15. Example 1. int main(){ 2. int i, s; 3. i=1; 4. s=1; 5. while(i<=10){ 6. s=s+i; 7. i++;} 8. printf(“%d”,s); 9. printf(“%d”,i); 10. } An Example Program & its slice w.r.t. <9, i>
- 16. Types of Slices StaticSlice: Statements that may affect value of a variable at a program point for all possible executions. Dynamic Slice: Statements that actually affect value of a variable at a program point for that particular execution. Backward Slice: Statements that might have affected the variable at a program point. Forward Slice: Statements that might be affected by the variable at a program point.
- 17. Example of ForwardSlice 1 main( ) 2 { 3 int i, sum; 4 sum = 0; 5 i = 1; 6 while(i <= 10) 7 { 8 sum = sum + 1; 9 ++ i; 10 } 11 printf(“%d”, sum); 12 printf(“%d”, i); 13 } An Example Program & its forward slice w.r.t. <5, i>
- 18. Types of Slicescont … Intra-Procedural Slice: for programs having only one procedure ◦ Not applicable for OOPs Inter-Procedural Slice: for programs having more than one procedure ◦ Applicable for OOPs
- 19. Applications of Slicing Debugging Program understanding Testing Software maintenance Complexity measurement Program integration Reverse engineering Software reuse
- 20. Debugging Guidelines Debuggingusually requires a thorough understanding of the program design. Debugging may sometimes require full redesign of the system. A common mistake novice programmers often make: ◦ not fixing the error but the error symptoms.
- 21. Debugging Guidelines Beaware of the possibility: ◦ an error correction may introduce new errors. After every round of error-fixing: ◦ regression testing must be carried out.
- 22. Program Analysis Tools An automated tool: ◦ takes program source code as input ◦ produces reports regarding several important characteristics of the program, ◦ such as size, complexity, adequacy of commenting, adherence to programming standards, etc.
- 23. Program Analysis Tools Some program analysis tools: ◦ produce reports regarding the adequacy of the test cases. There are essentially two categories of program analysis tools: ◦ Static analysis tools ◦ Dynamic analysis tools
- 24. Static Analysis Tools Static analysis tools: ◦ Assess properties of a program without executing it. ◦ Analyze the source code provide analytical conclusions.
- 25. Static Analysis Tools Whether coding standards have been adhered to? ◦ Commenting is adequate? Programming errors such as: ◦ uninitialized variables ◦ mismatch between actual and formal parameters. ◦ Variables declared but never used, etc.
- 26. Static Analysis Tools Code walk through and inspection can also be considered as static analysis methods: ◦ however, the term static program analysis is generally used for automated analysis tools.
- 27. Dynamic Analysis Tools Dynamic program analysis tools require the program to be executed: ◦ its behaviour recorded. ◦ Produce reports such as, extent of coverage achieved, adequacy of test cases, etc.
- 28. Summary Discussed differentdebugging approaches. ◦ Brute Force method ◦ Symbolic Debugger ◦ Backtracking ◦ Cause-Elimination Method ◦ Program Slicing Presented some debugging guidelines. Explained the Program Analysis Tools ◦ Static analysis tools ◦ Dynamic analysis tools 28
- 29. References 1. Rajib Mall,Fundamentals of Software Engineering, (Chapter – 10), Fifth Edition, PHI Learning Pvt. Ltd., 2018.
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