DAoTest.java

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {DbConfig.class})
@ActiveProfiles("DaoTest")
@Sql(executionPhase = Sql.ExecutionPhase.BEFORE_TEST_METHOD, scripts = "classpath:dao/TestData.sql")
public class PostgresEmbeddedDaoTestingApplicationTests {
  /* Here we have a static postgreSQL test container Class rule to make the instance used 
  for all test methods in the same test class , and we use @Transactional to avoid any dirty data changes between
  different test methods , where we pass our test database configuration ,
  ideally that should be loaded from external config file */
	@ClassRule
	public static PostgreSQLContainer postgreSQLContainer = (PostgreSQLContainer) new PostgreSQLContainer(
			"postgres:10.3")
			.withDatabaseName("test")
			.withUsername("user")
			.withPassword("pass").withStartupTimeout(Duration.ofSeconds(600));

	@Autowired
	private CustomerRepository customerRepository;

	@Test
	@Transactional
	public void contextLoads() {

		customerRepository.save(Customer.builder()
				.id(new Random().nextInt())
				.address("brussels")
				.name("TestName")
				.build());

		Assert.assertTrue(customerRepository.findCustomerByName("TestName") != null);
	}
}