unit-test-boundary-conditions

# Unit Testing Boundary Conditions and Edge Cases ## Overview Systematic patterns for testing boundary conditions, corner cases, and limit values in Java using JUnit 5. Covers numeric boundaries, string edge cases, collection states, floating-point precision, date/time limits, and off-by-one scenarios. ## When to Use - Numeric min/max limits, null/empty/whitespace inputs - Overflow/underflow validation, collection boundaries - Off-by-one errors, floating-point precision ## Instructions 1. **Identify boundaries**: List numeric limits (MIN_VALUE, MAX_VALUE, zero), string states (null, empty, whitespace), collection sizes (0, 1, many) 2. **Apply parameterized tests**: Use `@ParameterizedTest` with `@ValueSource` or `@CsvSource` for multiple boundary values 3. **Test both sides of boundaries**: Cover values just below, at, and just above each boundary 4. **Run tests after adding each boundary category** to catch issues early 5. **Verify floating-point precision**: Use `isCloseTo(expected, within(tolerance))` with AssertJ 6. **Test collection states**: Explicitly test empty (0), single (1), and many (>1) element scenarios 7. **Handle overflow/underflow**: Use `Math.addExact()` and `Math.subtractExact()` to detect arithmetic overflow 8. **Test date/time edges**: Verify leap years, month boundaries, timezone transitions 9. **Iterate based on failures**: When a boundary test fails, analyze the error to discover additional untested boundaries; add test cases for the newly discov...