Why software testing is a necessary step in SDLC? Differentiate between White-box testing and Black-box testing technique.

SDLC (Requirement → Design → Code → Test → Deploy → Maintain) needs testing because fixing a bug after deployment costs far more than catching it early, and police systems cannot afford wrong FIR or salary errors.

Why necessary: Finds defects, verifies requirements, ensures security, and builds trust before citizens use the portal.

Basis	White-box	Black-box
Knows code?	Yes — tests internal logic/paths	No — tests inputs vs expected outputs
Done by	Developers	Testers/users
Example	Check all IF branches in login function	Enter wrong password → "Invalid login" shown?
Catches	Logic, loop, security holes	Missing features, UI, requirement gaps

Good projects use both: white-box during coding, black-box before release (UAT).