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
- Identify boundaries: List numeric limits (MIN_VALUE, MAX_VALUE, zero), string states (null, empty, whitespace), collection sizes (0, 1, many)
- Apply parameterized tests: Use
@ParameterizedTestwith@ValueSourceor@CsvSourcefor multiple boundary values - Test both sides of boundaries: Cover values just below, at, and just above each boundary
- Run tests after adding each boundary category to catch issues early
- Verify floating-point precision: Use
isCloseTo(expected, within(tolerance))with AssertJ
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