How to test main class of Spring-boot application

问题:

I have a spring-boot application where my @SpringBootApplication starter class looks like a standard one. So I created many tests for all my functionalities and send the summary to sonarqube to see my coverage.

For my starter class Sonarqube tells me that I just have 60% coverage. So the average coverage is not good as expected.

My Test class is just the default one.

@RunWith(SpringRunner.class)
@SpringBootTest(classes = ElectronicGiftcardServiceApplication.class)
public class ElectronicGiftcardServiceApplicationTests {

    @Test
    public void contextLoads() {
    }
}

So how can I test my main class in the starter class of my application?

回答1:

All these answers seem overkill.
You don't add tests to make a metric tool happy.
Loading a Spring context of the application takes time. Don't add it in each developer build just to win about 0.1% of coverage in your application.
Here you don't cover only 1 statement from 1 public method. It represents nothing in terms of coverage in an application where thousands of statements are generally written.

First workaround : make your Spring Boot application class with no bean declared inside. If you have them, move them in a configuration class (for make them still cover by unit test). And then ignore your Spring Boot application class in the test coverage configuration.

Second workaround : if you really need to to cover the main() invocation (for organizational reasons for example), create a test for it but an integration test (executed by an continuous integration tool and not in each developer build) and document clearly the test class purpose :

import org.junit.Test;

// Test class added ONLY to cover main() invocation not covered by application tests.
public class MyApplicationIT {
   @Test
   public void main() {
      MyApplication.main(new String[] {});
   }
}

回答2:

You can do something like this

@Test
public void applicationContextLoaded() {
}

@Test
public void applicationContextTest() {
    mainApp.main(new String[] {});
}

回答3:

I had the same goal (having a test that runs the main() method) and I noticed that simply adding a test method like @fg78nc said will in fact "start" the application twice : once by spring boot test framework, once via the explicit invocation of mainApp.main(new String[] {}), which I don't find elegant.

I ended up writing two test classes : one with @SpringBootTest annotation and the empty test method applicationContextLoaded(), another one without @SpringBootTest (only RunWith(SpringRunner.class)) that calls the main method.

SpringBootApplicationTest

package example;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.boot.test.context.SpringBootTest;

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

  @Test
  public void contextLoads() {
  }
}

ApplicationStartTest

package example;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
public class ApplicationStartTest {
  @Test
  public void applicationStarts() {
    ExampleApplication.main(new String[] {});
  }
}

Overall, the application is still started two times, but because there is now two test classes. Of course, with only these two tests methods, it seems overkill, but usually more tests will be added to the class SpringBootApplicationTest taking advantage of @SpringBootTest setup.

回答4:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <mainClass>your.awesome.package.Application</mainClass> 
    </configuration>
</plugin>

If you aim for 100% coverage, one thing you can do is simply not having a main method at all. You still require a class annotated with @SpringBootApplication but it can be empty.

Be warned though as it has its drawbacks and other tools that rely on main can break.

回答5:

You can Mock SpringApplication since that is a dependency of the method under test. See how here. I.e.

import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.springframework.boot.SpringApplication;

import static org.powermock.api.mockito.PowerMockito.mockStatic;
import static org.powermock.api.mockito.PowerMockito.verifyStatic;

@RunWith(PowerMockRunner.class)
public class ElectronicGiftcardServiceApplicationTest {

    @Test
    @PrepareForTest(SpringApplication.class)
    public void main() {
        mockStatic(SpringApplication.class);
        ElectronicGiftcardServiceApplication.main(new String[]{"Hello", "World"});
        verifyStatic(SpringApplication.class);
        SpringApplication.run(ElectronicGiftcardServiceApplication.class, new String[]{"Hello", "World"});
    }

}