My notes on Java and libraries associated with Java. Notes in the public.

Concepts

Streams

• Can create stream of any type of Collection (Collection, List, Set)
• Stream<String> streamBuilder = Stream.<String>builder().add("a").add("b").add("c").build();
• Stream<String> streamGenerated = Stream.generate(() -> "element").limit(10);
• stream pipeline
  • source, intermediate operation(s) and a terminal operation.
• reduce()

Libraries

Spring Boot

https://roadmap.sh/spring-boot

• Spring Events - Observer Pattern
• Spring Cloud Stream

JUnit

https://junit.org/

Notes:

• By default, When each test function is run a new instance of the test class is instantiated. This means mocks declared on the class are “reset” for each test.

class TestCase {
    @Test
    void testFunction() {
      // Given

      // When

      // Then
      assertTrue()
      assumeFalse()
      assertEquals()
      assertArrayEquals()
      assertNotNull()
      assertNull()
    }
}

AssertJ

https://assertj.github.io/doc/

class TestCase {
    @Test
    void testFunction() {
      // Given

      // When

      // Then
      assertThat(frodo)
      .isNotEqualTo(sauron)
      .isIn(fellowshipOfTheRing);

      assertThat(frodo.getName())
      .startsWith("Fro")
      .endsWith("do")
      .isEqualToIgnoringCase("frodo");

      assertThat(fellowshipOfTheRing)
      .hasSize(9)
      .contains(frodo, sam)
      .doesNotContain(sauron);
    }

Mockito

https://site.mockito.org/

@RunWith(SpringRunner.class)
public class MockBeanAnnotationIntegrationTest {
    
    @MockBean
    UserRepository mockRepository;
    
    @Autowired
    ApplicationContext context;
    
    @Test
    public void givenCountMethodMocked_WhenCountInvoked_ThenMockValueReturned() {
        Mockito.when(mockRepository.count()).thenReturn(123L);

        UserRepository userRepoFromContext = context.getBean(UserRepository.class);
        long userCount = userRepoFromContext.count();

        Assert.assertEquals(123L, userCount);
        Mockito.verify(mockRepository).count();
    }
}

wiremock

https://wiremock.org/