Comprehensive Guide to Debugging in Software Testing"

Software Debugging Dr. Durga Prasad Mohapatra Professor National Institute of Technology Rourkela

Debugging  Once errors are 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.

Some Debugging Approaches • Brute Force method • Symbolic Debugger • Backtracking • Cause-Elimination Method • Program Slicing 3

Brute-force method  This is 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.

Symbolic Debugger  Brute force 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.

Symbolic Debugger  Using a 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.

Backtracking  This is a fairly common approach.  Beginning at the statement where an error symptom has been observed: ◦ source code is traced backwards until the error is discovered.

Example int main( ){ int i, j, s; i=1; while(i<=10){ s=s+i; i++; j=j++;} printf(“%d”,s); }

Backtracking  Unfortunately, as the number of source lines to be traced back increases, ◦ the number of potential backward paths increases ◦ becomes unmanageably large for complex programs.

Cause-elimination method  In this 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.

Program Slicing  This technique 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.

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.

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>

Program Dependence Graph 1 5 6 11 8 3 12 4 9 Control Dep Edge Data Dep Edge

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>

Types of Slices Static Slice: 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.

Example of Forward Slice 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>

Types of Slices cont …  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

Applications of Slicing  Debugging  Program understanding  Testing  Software maintenance  Complexity measurement  Program integration  Reverse engineering  Software reuse

Debugging Guidelines  Debugging usually 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.

Debugging Guidelines  Be aware of the possibility: ◦ an error correction may introduce new errors.  After every round of error-fixing: ◦ regression testing must be carried out.

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.

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

Static Analysis Tools  Static analysis tools: ◦ Assess properties of a program without executing it. ◦ Analyze the source code  provide analytical conclusions.

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.

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.

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.

Summary  Discussed different debugging 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

References 1. Rajib Mall, Fundamentals of Software Engineering, (Chapter – 10), Fifth Edition, PHI Learning Pvt. Ltd., 2018.

Comprehensive Guide to Debugging in Software Testing"

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