How to test main class of Spring-boot application

Question

I have a spring-boot application where my @SpringBootApplication starter class looks like a standard one. So I created many tests for all my functi

Answer 1

Even though this question has been answered extensively I had a use case that is not covered here that is perhaps interesting to share. I am validating some properties at startup and I wanted to assert that the application would fail to start if these properties were configured wrong. In JUnit4 I could have done something like this:

@ActiveProfiles("incorrect")
@SpringBoot
public class NetworkProbeApplicationTest {

    @Test(expected=ConfigurationPropertiesBindException.class)
    public void contextShouldNotLoadWhenPropertiesIncorrect() {
    }
}

But in JUnit5 you can no longer add the "expected" value to your @Test annotation and you have to do it differently. And since I wanted to start the application with an incorrect set of properties I needed to pass in which profile to use as a main() argument. I could not really find this documented anywhere, but passing in arguments through the main() method requires you to prefix your arguments with a double hyphen and separate the key and value with an equals sign. A complete test would look like this:

import org.junit.jupiter.api.Test;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.context.properties.ConfigurationPropertiesBindException;

import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

public class NetworkProbeApplicationTest {

    @Test
    public void contextShouldNotLoadWhenPropertiesIncorrect() {
        Exception exception = assertThrows(ConfigurationPropertiesBindException.class, () -> {
            SpringApplication.run(NetworkProbeApplication.class, "--spring.profiles.active=incorrect");
        });

        String expectedMessage = "Error creating bean with name 'dnsConfiguration': Could not bind properties to 'DnsConfiguration' : prefix=dns";

        assertTrue(exception.getMessage().contains(expectedMessage));
    }
}