This is based on the Test-Driven Development with Spring Boot talk given in SpringOne 2017

• Test-driven development (TDD) is a software development process that relies on the repetition of a very short development cycle of Red, Green, Refactor

• Start a new "Web" Spring Boot project from Spring Boot Initialzr

• The CarController, given a correct car name, i.e. "/cars/prius", should return success (200) and Car data in JSON format in the response body

• The CarController, given a non-existent car name, i.e. "/cars/nocar", should return failure (404)

• (Optional) The CarController, given a new car, should add it to the system and return success (201) with response body containing newly added car

• Use @WebMvcTest, which automatically configures MockMvc object

• Given that it is a unit testing, you should mock CarService object - think about which one to use, @Mock or @MockBean

• In Spring, all exceptions should be RunTimeException

• Observe how much time this test takes and see if Tomcat gets started or not

• The CarService's getCarDetails method, given a correct car name, "prius", should return Car object

• The method, given a non-existent car name, "nocar", should throw CarNotFoundException

• (Optional) The CarService's addCar(Car car) method should add it to the system and return added Car

• Since this is a unit testing, you should mock CarRepository object

• Start with testing with Spring using @RunWith(SpringRunner.class) (using Spring testing framework) and then refactor it with @RunWith(MockitoJUnitRunner.class) and think about which one is a better practice

• If you experience the following error, it is because you have not handle the case where CarRepository's findByName(..) method returns null.

  java.lang.AssertionError: Expected exception: com.example.demotdd5.CarNotFoundException
  
  ...
  org.h2.jdbc.JdbcSQLException: Database is already closed (to disable automatic closing at VM shutdown, add ";DB_CLOSE_ON_EXIT=FALSE" to the db URL) [90121-197]
  at org.h2.message.DbException.getJdbcSQLException(DbException.java:357)
  at org.h2.message.DbException.get(DbException.java:179)
  at org.h2.message.DbException.get(DbException.java:155)
  

• The CarRepository's findByName(..) method should return a Car given a valid car name

• (Optional) The CarRepository's save(..) method should return a Car give a Car object

• Use @DataJpaTest annotation, which provides TestEntityManager

• When your test fails below fails with org.springframework.orm.jpa.JpaSystemException: No default constructor for entity: .., it means your Car class does not have a default constructor

      @Test
      public void findByName_should_return_car_given_valid_car() 
                throws Exception {
  
      // arrange
      testEntityManager.persistAndFlush(new Car("camry", "regular"));
      testEntityManager.clear();
  
      // act and assert
      Car car = carRepository.findByName("camry");
      assertThat(car).isEqualTo(new Car("camry", "regular"));
  
      // verify
  }
  

• The CarService's getCarDetails(..) method should return an item from a cache if it gets called more than once

• The way you can test the caching behavior is to call CarService's getCarDetails(..) method twice and then see if it called CarRepository's findByName(..) method once

• The application, when accessed with "/cars/prius", should return success (200)

  • Assert that return status is 200
  • Assert that content type returned MediaType.APPLICATION_JSON_UTF8
  • Assert that the body returns Car, name and type of which are "prius" and "hybrid" respectively

• Use @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
• Observe how much this test takes, also observe that this test starts Tomcat