Software Testing

Introduction

• Software Testing: The process of executing a program== with the ==intent of finding errors.

• Ensures software meets requirements, is defect-free, reliable, and fit for use.
• Conducted at different levels of SDLC.

Objectives of Testing

• Detect defects before delivery.

• Ensure requirements are met.

• Increase reliability and quality.

• Validate functionality, performance, and security.
• Reduce maintenance cost.
• Build user confidence.

Principles of Testing

1. Testing shows presence of defects, not absence.

2. Exhaustive testing is impossible.

3. Testing should start early (shift-left).
4. Defects cluster in few modules.
5. Pesticide paradox: repeated tests lose effectiveness.

6. Testing is context dependent.

7. Absence of errors fallacy: bug-free but useless software still fails.

Software Testing Life Cycle (STLC)

1. Requirement Analysis – Identify testable requirements.
2. Test Planning – Define scope, objectives, resources, risks.
3. Test Case Development – Write test cases, test scripts, test data.
4. Environment Setup – Hardware, software, network readiness.
5. Test Execution – Run test cases, log defects.
6. Test Closure – Deliver reports, metrics, lessons learned.

Levels of Testing ⭐

1. Unit Testing ⭐

   • Tests individual components (functions, classes).

   • Usually automated.
   • Done by developers.
2. Integration Testing ⭐

   • Tests interaction between integrated modules.

   • Approaches:
     • Big-Bang Integration
     • Top-Down
     • Bottom-Up
     • Sandwich/Hybrid
3. System Testing

   • Tests complete system as a whole.

   • Validates functional + non-functional requirements.
4. Acceptance Testing

   • Done by client/user.

   • Confirms system meets business needs.
   • Types:

     • Alpha Testing (internal users). ⭐

     • Beta Testing (external users). ⭐

Types of Testing

Functional Testing

• Validates software functions as per requirements.
• Examples: Unit testing, integration, system, UAT, regression, smoke, sanity.

Non-Functional Testing

• Checks performance, scalability, security, usability, reliability.
• Examples: Load testing, stress testing, volume testing, compatibility, recovery testing.

Maintenance Testing

• After deployment, when software is modified.
• Regression Testing – ensures old functionality works after changes.
• Re-testing – validates fixes of specific defects.

Two Testing Approaches ⭐

1. White Box Testing (Structural) ⭐

   • Internal logic tested.

   • Techniques:
     • Statement Coverage
     • Branch Coverage
     • Path Coverage
     • Loop Testing

2. Black Box Testing (Functional) ⭐

   • Ignores internal code, focuses on inputs/outputs.

   • Techniques:
     • Equivalence Partitioning

     • Boundary Value Analysis

     • Decision Table Testing

     • State Transition Testing
3. Grey Box Testing ⭐
   • Combines white + black box.
   • Tester has partial knowledge of system.

Test Documentation

• Test Plan – strategy, objectives, resources.
• Test Case Specification – input, expected output, actual output.
• Test Data – sample inputs for testing.
• Test Execution Report – results of test runs.
• Defect Report – bug ID, description, severity, status.
• Test Summary Report – overall testing status, coverage, pass/fail ratio.

Automated vs Manual Testing

• Manual Testing: Executed by human testers, good for exploratory/ad-hoc testing.
• Automated Testing: Uses tools/scripts for regression, load, performance tests.
• Tools: Selenium, JUnit, TestNG, QTP, LoadRunner, JMeter.

Defect Lifecycle (Bug Life Cycle)

1. New → Assigned → Open → Fixed → Retest → Verified → Closed.
2. If not fixed: can be Reopened, Deferred, or Rejected.

Metrics in Testing

• Defect Density = Defects / Size of software.
• Test Coverage = (Executed tests / Total tests) × 100.
• Defect Removal Efficiency (DRE) = (Defects removed / Total defects) × 100.
• MTTF (Mean Time to Failure).

Standards for Testing

• IEEE 829 – Test documentation.
• ISO/IEC/IEEE 29119 – Software testing standards.
• ISO/IEC 9126 – Software quality metrics.

Challenges in Testing

• Limited time and resources.
• Changing requirements.
• Test environment issues.
• Maintaining automation scripts.
• Communication gaps with stakeholders.

Best Practices

• Start testing early.
• Maintain traceability matrix (requirements ↔ test cases).
• Prioritize test cases by risk and criticality.
• Use automation for regression and performance tests.
• Regular reviews of test cases and plans.
• Continuous testing in DevOps/Agile.