@Service
public class KeyService {

    @Cacheable("keyCache")
    public String getKey() {
        return "fakeKey";
    }
}

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

    @Autowired
    private KeyService keyService;

    @Test
    public void shouldReturnTheSameKey() {

        Mockito.when(keyService.getKey()).thenReturn("key1", "key2");

        String firstCall = keyService.getKey();
        assertEquals("key1", firstCall);

        String secondCall = keyService.getKey();
        assertEquals("key1", secondCall);
    }

    @EnableCaching
    @Configuration
    static class KeyServiceConfig {

        @Bean
        KeyService keyService() {
            return Mockito.mock(KeyService.class);
        }

        @Bean
        CacheManager cacheManager() {
            return new ConcurrentMapCacheManager("keyCache");
        }
    }
}

@Service
public class KeyService {

    @Cacheable("keyCache")
    public String getKey(String param) {
        return "fakeKey";
    }
}

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

    @Autowired
    private KeyService keyService;

    @Test
    public void shouldReturnTheSameKey() {

        Mockito.when(keyService.getKey(Mockito.anyString())).thenReturn("key1", "key2");

        String firstCall = keyService.getKey("xyz");
        assertEquals("key1", firstCall);

        String secondCall = keyService.getKey("xyz");
        assertEquals("key1", secondCall);
    }

    @EnableCaching
    @Configuration
    static class KeyServiceConfig { //The same code as shown above }
}