User Registration Integration Tests

Write integration tests for a Spring Boot user registration flow. The application has:

• UserController with endpoints:
  • POST /api/users/register -- accepts {"username": "...", "email": "...", "password": "..."}, returns 201 with the created user (without password)
  • GET /api/users/{id} -- returns user profile
• UserService handles registration logic: validates input, checks for duplicate email, hashes password, saves via UserRepository
• UserRepository extends JpaRepository<User, Long>
• The production database is PostgreSQL

Output

Produce a Java test file at src/test/java/com/example/users/UserRegistrationIntegrationTest.java.

Also produce src/test/resources/application-test.yml with the test database configuration.

Test at minimum:

1. Registering a new user returns 201 and the user can be retrieved via GET
2. Registering with a duplicate email returns 409 Conflict
3. Registering with invalid input (missing username) returns 400
4. Getting a nonexistent user returns 404

Do not produce the application source code -- only the test file and test configuration.