Differentiate Between Black Box and White Box Testing. Explain Different Stages of Testing.

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Difference Between Black Box and White Box Testing

Black Box Testing tests the software without knowledge of internal code, while White Box Testing tests the software with full knowledge of internal structure and logic.

Criteria	Black Box Testing	White Box Testing
Knowledge	No knowledge of internal code	Full knowledge of internal code
Focus	Tests functionality (what it does)	Tests logic and structure (how it does)
Performed by	Testers / End users	Developers
Also called	Functional testing / Closed box testing	Structural testing / Glass box testing
Techniques	Equivalence partitioning, Boundary value analysis	Statement coverage, Branch coverage, Path testing
Basis	Based on requirements and specifications	Based on source code and design
Programming knowledge	Not required	Required
Level of testing	Higher level (system, acceptance)	Lower level (unit testing)

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Different Stages of Testing

Testing is performed in multiple stages, each targeting a different level of the software system to ensure quality at every layer.

a) Unit Testing

• Tests individual modules or components in isolation
• Performed by developers during coding phase
• Verifies that each unit works correctly on its own
• Uses white box testing techniques

b) Integration Testing

• Tests the interaction between combined modules
• Detects interface defects between integrated units
• Approaches: Top-down, Bottom-up, and Big Bang integration
• Ensures modules work together as expected

c) System Testing

• Tests the complete integrated system as a whole
• Verifies the system meets functional and non-functional requirements
• Performed in an environment similar to production
• Includes performance testing, security testing, and usability testing

d) Acceptance Testing

• Tests whether the system is acceptable to the end user/client
• Two types:
  • Alpha Testing – done at developer's site by internal users
  • Beta Testing – done at client's site by actual users
• Final stage before software is delivered

e) Regression Testing

• Re-testing the software after modifications or bug fixes
• Ensures that new changes have not introduced new defects
• Performed at every stage when changes are made

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Conclusion

Testing stages move from small units → integrated modules → full system → user acceptance, ensuring defects are caught early and software quality is maintained at every level. Black box and white box testing complement each other to provide comprehensive test coverage.