unit-test-boundary-conditions

Boundary testing in JUnit 5 involves writing parameterized tests using junit-jupiter-params to validate behavior at limits—null inputs, empty collections, minimum/maximum numeric values, and whitespace. Use @ParameterizedTest with @ValueSource, @CsvSource, or @MethodSource to systematically cover edge cases and verify assertions with AssertJ.

Edge cases include null or empty inputs, minimum and maximum values for numeric types, overflow/underflow conditions, whitespace-only strings, zero-length collections, and boundary transitions. Testing these with parameterized JUnit 5 tests ensures code handles unexpected inputs gracefully and prevents runtime failures.

Yes. Parameterized tests in JUnit 5 pair well with AssertJ assertions to validate multiple boundary scenarios in a single test method. Define test parameters using @ValueSource or @CsvSource, then use AssertJ's fluent API to assert expected behavior across all edge cases and boundary transitions.

Add junit-jupiter and junit-jupiter-params dependencies to your Maven pom.xml or Gradle build.gradle. For Maven, configure the Maven Surefire Plugin; for Gradle, use the test task with JUnit Platform support. Both automatically discover and run parameterized @ParameterizedTest methods with boundary value inputs.

Boundary testing isolates validation of code behavior at extreme or exceptional inputs—nulls, empty states, and limits—where bugs commonly hide. Parameterized boundary tests decouple edge-case coverage from happy-path logic, increasing test clarity and reducing the risk of untested failure modes.