White Box Techniques

Statement Coverage

Mỗi line code executed at least once.

def discount(price, vip):
    if vip:
        return price * 0.8
    return price * 0.95

Test 1: vip=True → covers if branch. Test 2: vip=False → covers else. 2 tests = 100% statement coverage.

Branch Coverage

Mỗi branch (true/false of each condition) covered. Same example above → same 2 tests suffice.

Condition Coverage

Each boolean sub-condition gets both true/false.

if vip and country == "VN":
    return discount

• (vip=T, country=VN) → both T.
• (vip=F, country=US) → both F.

2 tests cover condition coverage.

Path Coverage

Every possible execution path.

• Exponential in nested conditions.
• Rarely 100% feasible.

MC/DC (Modified Condition/Decision Coverage)

Aviation/safety standard. Each condition independently affects outcome.

Loop Coverage

• 0 iteration.
• 1 iteration.
• > 1 iteration.
• Boundary (N-1, N, N+1) if N has limit.

Tools

• Jest --coverage (JS).
• Coverage.py (Python).
• JaCoCo (Java).
• Slather (iOS).

Anti-pattern

• 100% line coverage = no quality assurance. Test execute code but no assert.
• Skip difficult code (catch block) → low value coverage.
• Mock too much → don't test real behavior.

Mutation testing

Insert random bug → does test catch?

• Stryker (JS), PIT (Java).
• Real measure of test quality.
• Run weekly, not every commit (slow).

VN context

Banking critical service: MC/DC mandatory. SBV inspector ask for evidence.