Spring Boot unit test runs the whole program

Csaba Faragó :

I would like to implement an integration test with Spring Boot. I start with the spring-boot-starter-test dependency, version 2.2.5.RELEASE.

I have the following component:

@Component
public class MyMath {

    public int add(int a, int b) {
        return a + b;
    }

}

The main program looks like this:

@SpringBootApplication
public class Main implements CommandLineRunner {

    public static void main(String[] args) {
        SpringApplication.run(Main.class, args);
    }

    @Autowired
    private MyMath myMath;

    @Override
    public void run(String... args) throws Exception {
        System.out.println(myMath.add(2, 3));
    }

}

It works as expected - so far, so good. I would like to add a unit test:

@RunWith(SpringRunner.class)
@SpringBootTest
public class MyMathTest {

    @Autowired
    private MyMath myMath;

    @Test
    public void testSaveAndList() {
        assertEquals(5, myMath.add(2, 3));
    }

}

This also works, but according to the log it executes the whole program. I don't want to run the program itself, just the MyMath.add() function. How can I do that?

I tried the following so far:

@RunWith(SpringJUnit4ClassRunner.class) provided the same result.
Omitting @SpringBootTest results NoSuchBeanDefinitionException.
Reformatting the code to have bean instead of component like below it works.

MyMath without annotation:

public class MyMath {

    public int add(int a, int b) {
        return a + b;
    }

}

Main remains the same.

@Configuration
public class AppConfig {

    @Bean
    public MyMath getMyMath() {
        return new MyMath();
    }
}

And the test:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = AppConfig.class)
public class MyMathTest {

    @Autowired
    private MyMath myMath;

    @Test
    public void testSaveAndList() {
        assertEquals(5, myMath.add(2, 3));
    }

}

So what I cannot do is to test a component without running the whole program. Could any help me? Thanks!

pvpkiran :

You do not need to refactor your code. Just keep the MyMath class as it is

@Component
public class MyMath {

    public int add(int a, int b) {
        return a + b;
    }
}

Change your test class like this

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = MyMath.class)
public class MyMathTest {

    @Autowired
    private MyMath myMath;

    @Test
    public void testSaveAndList() {
        assertEquals(5, myMath.add(2, 3));
    }

}

This becomes a bit complex if your MyMath class has other dependencies autowired. Then you have to use mocks.