Maven uses convention, lifecycle phases, and XML project metadata. Gradle uses a programmable build model and supports Groovy or Kotlin DSLs.

mvn test
mvn package

./gradlew test
./gradlew build

A build should be reproducible: dependency versions should be controlled, generated artifacts should be deterministic where practical, and CI should run the same essential verification steps developers use locally.

Unit tests isolate a small behavior and should be fast and deterministic. Integration tests verify interactions with real components such as databases, message brokers, HTTP servers, or filesystems.

@Test
void calculatesTotal() {
    Cart cart = new Cart();
    cart.add(new Item("Book", 500));

    assertEquals(500, cart.total());
}

A healthy test strategy uses the cheapest test that provides useful confidence while maintaining enough realistic integration coverage to catch wiring and infrastructure failures.

A test double replaces a real dependency. A stub supplies predetermined answers, a fake provides a lightweight working implementation, and a mock is commonly used to verify interactions.

Over-mocking makes tests brittle when they verify implementation details.

UserRepository repository = new InMemoryUserRepository();
UserService service = new UserService(repository);

assertTrue(service.exists("u-1"));

Prefer real lightweight implementations where practical. Mock external systems when setup is expensive or unreliable.

Production Java projects commonly combine formatting, static analysis, tests, dependency scanning, and code review.

Useful checks include compiler warnings, static analyzers, formatting tools, dependency vulnerability scanning, and CI tests.

mvn test
mvn verify

Quality gates should fail the build for issues that matter. Avoid hundreds of noisy warnings that developers learn to ignore.