Spring test module - spring-boot-starter-test

Overview

Spring Boot offers strong built-in support for testing. The spring-boot-starter-test starter includes various testing features, helping developers write tests without complicated setup.

spring-boot-starter-test

• Spring Boot provides the spring-boot-starter-test starter for integration testing
• automatically includes key libraries such as JUnit 5, Mockito, AssertJ, Hamcrest, and Spring Test

Main libraries included:

Library	Description	Notes
JUnit 5	The leading Java testing framework	Using version 5 (which is different from 4). Version 3 is not used much. - Ver 5 is the standard - Explicitly state diff. version if you need to
Mockito	Creates mock objects	Used to disconnect (단절) layers for unit testing, slice testing
AssertJ	A library used for validation & gives assertion syntax.	- Provides readable, fluent assertion syntax - Used together with JUnit. Friendly to developers
Hamcrest	Matcher-based assertion tool	- alternative to AssertJ for assertions - style is closer to english - what to choose is just team/personal preference
Spring Test	Supports Spring ApplicationContext and MockMvc	Enables dependency injection (@Autowired) in tests by loading the Spring container (ApplicationContext) - [[IoC (Inversion of Control)#ApplicationContext|IoC (Inversion of Control) - ApplicationContext]]
JSONassert	Useful for comparing JSON responses	Intelligently compares two JSON strings, ignoring formatting and field order, to check if they are semantically the same
Spring Boot Test	Supports integration testing in Spring Boot	- Simplifies integration testing with @SpringBootTest. - Provides “slice test” annotations (e.g., @WebMvcTest, @DataJpaTest) to test specific application layers quickly.

Key Testing Annotations

Basically ALL OF THESE ARE IMPORTANT AND YOU NEED TO KNOW EVERYTHING

Spring provides various annotations to simplify writing tests. Key annotations include:

Annotation	Library	Description	Common Test Type(s)
@SpringBootTest	Spring Boot Test	Loads the entire application context for testing	Integration, Functional
@WebMvcTest	Spring Boot Test	Loads only the web layer (e.g., Controller) for slice testing	Slice (Web Layer)
@DataJpaTest	Spring Boot Test	Loads only the persistence layer (JPA) for slice testing - Data Access (Repository) Layer Testing	Slice (Data Layer)
@MockBean	Spring Boot Test	Replaces a Spring bean with a Mockito mock in the context	Slice, Integration
@SpyBean	Spring Boot Test	Wraps a real Spring bean with a Mockito spy in the context	Slice, Integration
@Test	JUnit 5	Marks a method as a test method that should be run	All (Unit, Slice, etc.)
@BeforeEach	JUnit 5	Runs a setup method before each @Test method	All (Unit, Slice, etc.)
@AfterEach	JUnit 5	Runs a teardown method after each @Test method	All (Unit, Slice, etc.)

• @SpringBootTest
  • loads the entire application context, which can be slow.
  • Use it only when necessary, and prefer slice tests like @WebMvcTest or @DataJpaTest for faster, more focused testing.
• JUnit 5 → explains more about the key annotations

Example Code

@SpringBootTest
class OrderServiceTest {
 
    @Autowired
    private OrderService orderService;
 
    @Test
    void createOrder_ShouldSucceed() {
        // given
        OrderRequest request = new OrderRequest("Americano", 2);
 
        // when
        Order order = orderService.createOrder(request);
 
        // then
        assertThat(order.getQuantity()).isEqualTo(2);
    }
}