Program Testing And Maintenance (Copy)

12.3.1 Ways of Avoiding and Exposing Faults in Programs

• Human Error in Programming
  • Programmers make mistakes, which lead to faults in software.
  • Goal: Minimize errors and detect as many as possible before deployment.
• Consequences of Faults
  • Some major banks faced customer lockouts due to software faults.
  • Airlines have had to cancel flights due to programming errors.
  • A prison system mistakenly released prisoners early for 15 years due to a faulty program.
• Fault Prevention Strategies
  • Comprehensive program specifications: A detailed and rigorous specification should be created during the analysis phase.
  • Formal Methods: Techniques like structure charts, state-transition diagrams, and pseudocode help in design and testing.
  • Programming disciplines: Concepts such as encapsulation, information hiding, and exception handling reduce faults.
• Fault Exposure in Testing
  • Testing can only reveal faults; it cannot guarantee a completely error-free program.
  • Large and complex programs might have undetected faults despite rigorous testing.
  • Errors found after deployment must be corrected through maintenance.

12.3.2 Location, Identification, and Correction of Errors

• Types of Errors
  • Syntax Errors: Errors in the grammar of the programming language. These are detected by compilers or interpreters.
    • Example: A variable name is misspelled (vvalue2 instead of value2).
  • Logic Errors: The program runs but does not produce the expected results.
    • Example: A directional movement program incorrectly updates the X coordinate instead of Y.
  • Run-time Errors: Errors that occur while the program is running, such as division by zero.
    • Example: A division operation where the denominator becomes zero.
• Debugging Tools
  • Trace Tables: Track variable values throughout execution to detect logic errors.
  • Integrated Development Environments (IDEs): Provide debugging tools, such as breakpoints and step-by-step execution.

12.3.3 Program Testing

• Testing is Continuous
  • Begins as soon as the program is written.
  • Should be documented to prove robustness and readiness.
• Test Strategy
  • A high-level overview of required testing.
  • Shows how and when testing will be conducted.
• Test Plan
  • Detailed documentation listing all testing stages and test cases.
  • Includes test data, expected results, and actual results.
• Types of Testing
  • White-box Testing: Tests the internal structure and logic of the program.
  • Black-box Testing: Focuses on inputs and expected outputs without considering internal logic.
  • Integration Testing: Ensures different program modules function together.
  • Stub Testing: Uses dummy modules for testing when real modules are unavailable.
• Final Testing Phases
  • Alpha Testing: Conducted in-house by the development team.
  • Beta Testing: Done by external users before the program’s official release.
  • Acceptance Testing: Ensures the software meets customer requirements before full deployment.

12.3.4 Program Maintenance

• Understanding Maintenance
  • Unlike physical equipment, programs do not degrade over time.
  • However, they might fail under unforeseen circumstances.
  • Users may require new features, necessitating updates.
• Types of Program Maintenance
  • Corrective Maintenance: Fixes errors that appear during use.
    • Example: A program crashes due to a previously undetected run-time error.
  • Perfective Maintenance: Enhances program performance.
    • Example: Optimizing an algorithm to improve execution speed.
  • Adaptive Maintenance: Modifies a program to meet new requirements.
    • Example: Updating a program to support voice commands in addition to keyboard input.

Types of Test Data

• Normal Test Data
  • Data that is expected and should be correctly processed.
  • Example: Testing a function that adds two numbers with inputs 10 and 20.
• Abnormal Test Data
  • Data that should be rejected by the program.
  • Example: Inputting a string ("twenty") into a numeric field.
• Extreme Test Data
  • Data at the edge of acceptable limits.
  • Example: If an input range is 12-32, testing with 12 and 32.
• Boundary Test Data
  • Data at the boundary of acceptable and unacceptable inputs.
  • Example: If the valid range is 12-32, testing with 11 (invalid) and 12 (valid).

Practical Testing Example

• Sample Calculation Procedure

  PROCEDURE calculation(number1, number2, sign)
  CASE sign OF
    '+' : answer ← number1 + number2
    '-' : answer ← number1 - number2
    '*' : answer ← number1 * number2
    '/' : answer ← number1 / number2
    OTHERWISE answer ← 0
  ENDCASE
  IF answer <> 0 THEN OUTPUT answer ENDIF
  ENDPROCEDURE
  

• Test Cases for Above Procedure

Conclusion

• Rigorous testing is essential to ensure program reliability and user satisfaction.
• A well-structured maintenance plan ensures software remains functional, efficient, and adaptable.
• Various testing techniques and data types help identify and fix errors at different stages of development.
• Effective program testing and maintenance contribute to long-term software success.