Integration test for single Spring Boot @Service class

Question

I'm writing an integration test for this Spring Boot @Service bean

import org.springframework.stereotype.Service;
import org.thymeleaf.ITemplateEngine;
import org.thymeleaf.context.Context;

import java.util.Locale;
import java.util.Map;

@Service
public class ThymeLeafEmailTemplateService implements EmailTemplateService {

    private final ITemplateEngine springTemplateEngine;

    public ThymeLeafEmailTemplateService(ITemplateEngine springTemplateEngine) {
        this.springTemplateEngine = springTemplateEngine;
    }

    public String generateEmailBody(String template, Map<String, Object> variables) {
        Context context = new Context(Locale.getDefault(), variables);
        return springTemplateEngine.process(template, context);
    }
}

Currently, the test class is defined as shown below

@SpringBootTest
class ThymeLeafEmailTemplateServiceTests {


    @Autowired
    private EmailTemplateService service;

    @Test
    void generateTaskNotificationEmail() {
      var output = service.generateEmailBody("/template", Map.of());
      assertEquals("Expected Output", output);
    }
}

A problem with this approach is that it's very slow/inefficient because the entire application context is loaded, but I really only need the service being tested and its dependencies.

If I change the test class' annotations to

@SpringBootTest
@ContextConfiguration(classes = ThymeLeafEmailTemplateService.class)

the test fails, because the dependency ITemplateEngine springTemplateEngine does not exist. I could add this dependency to classes (the list of beans to create), but this seems like a very brittle approach.

Is there an efficient way to integration test a single @Service?

Note:

I know I could mock ITemplateEngine springTemplateEngine and write a unit test instead, but I want to test the template's actual output, so this approach won't work

Answer 1

You can use

@WebMvcTest(ThymeLeafEmailTemplateService.class)

This will load only that bean in your application context along with any default Spring configuration beans.