public interface ICalculator {

    int sum(int x, int y);
    int minus(int x, int y);

    void init();
}

@Component
@RequiredArgsConstructor
public class Calculator {

    private final ICalculator iCalculator;


    public int sum(int x, int y){
        // 시세 반영 시킨후 계산
        this.iCalculator.init();
        return this.iCalculator.sum(x,y);
    }

    public int minus(int x, int y){
        this.iCalculator.init();
        return this.iCalculator.minus(x, y);
    }
}

@Component
@RequiredArgsConstructor
public class DollarCalculator implements ICalculator {

    private int price = 1;
    private final MarketApi marketApi;

    public void init(){
        this.price = marketApi.connect();
    }
    @Override
    public int sum(int x, int y) {
        x *= price;
        y *= price;
        return x + y;
    }

    @Override
    public int minus(int x, int y) {
        x *= price;
        y *= price;
        return x - y;
    }
}

@Component
public class MarketApi {

    public int connect(){
        return 1100;
    }
}

@RestController
@RequestMapping("/api")
@RequiredArgsConstructor
public class CalculatorApiController {

    private final Calculator calculator;

    @GetMapping("/sum")
    public int sum(@RequestParam int x, @RequestParam int y){
        return calculator.sum(x,y);
    }

    @PostMapping("/minus")
    public Res minus(@RequestBody Req req){

        int result = calculator.minus(req.getX(), req.getY());

        Res res = new Res();
        res.setResult(result);
        res.setResponse(new Res.Body());
        return res;
    }
}

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Req {
    private int x;
    private int y;
}

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Res {
    private int result;

    private Body response;

    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public static class Body{
        private String resultCode = "OK";
    }
}

Test 코드

@SpringBootTest
@Import({MarketApi.class, DollarCalculator.class})
public class DollarCalculatorTest {

    @MockBean
    private MarketApi marketApi;

    @Autowired
    private DollarCalculator dollarCalculator;

    @Test
    public void dollarCalculatorTest(){
        Mockito.when(marketApi.connect()).thenReturn(3000);
        // 이게 없으면 값이 그냥 20으로 나옴
        dollarCalculator.init();

        int sum = dollarCalculator.sum(10, 10);
        int minus = dollarCalculator.minus(10,10);

        Assertions.assertEquals(60000, sum);
        Assertions.assertEquals(0, minus);
    }
}

@WebMvcTest(CalculatorApiController.class)
@AutoConfigureWebMvc
// Calculator가 ICalculator 주입 받고 있어서 Dollar*.class 넣어 주었고
// Dollar 안 MarketApi는 Mock으로 처리
@Import({Calculator.class, DollarCalculator.class })
public class CalculatorApiControllerTest {

    @MockBean
    private MarketApi marketApi;

    @Autowired
    private MockMvc mockMvc;

    @BeforeEach
    private void init(){
        Mockito.when(marketApi.connect()).thenReturn(3000);
    }

    @Test
    public void sumTest() throws Exception {
        // http://localhost:8080/api/sum

        mockMvc.perform(
                MockMvcRequestBuilders.get("http://localhost:8080/api/sum")
                        .queryParam("x","10")
                        .queryParam("y", "10")
        ).andExpect(
                MockMvcResultMatchers.status().isOk()
        ).andExpect(
                MockMvcResultMatchers.content().string("60000")
        ).andDo(MockMvcResultHandlers.print());
    }

    @Test
    public void minusTest() throws Exception {

        Req req = new Req();
        req.setX(10);
        req.setY(10);

        String json = new ObjectMapper().writeValueAsString(req);

        mockMvc.perform(
                MockMvcRequestBuilders.post("http://localhost:8080/api/minus")
                        .contentType(MediaType.APPLICATION_JSON)
                        .content(json)
        ).andExpect(
                MockMvcResultMatchers.status().isOk()
        ).andExpect(
                MockMvcResultMatchers.jsonPath("$.result").value("0")
        ).andExpect(
                MockMvcResultMatchers.jsonPath("$.response.resultCode").value("OK")
        ).andDo(
                MockMvcResultHandlers.print()
        );
    }
}

각각 어노테이션 및 테스트 코드 동작 원리를 제대로 이해하자..

아직 헷갈림