Using junit test to pass command line argument to Spring Boot application

Question

I have a very basic Spring Boot application, which is expecting an argument from command line, and without it doesn\'t work. Here is the code.

@SpringBootApplica         


        

Answer 1

As mentioned in this answer, Spring Boot currently doesn't offer a way to intercept/replace the DefaultApplicationArguments that it uses. A natural-Boot-way that I used to solve this was to enhance my runner logic and use some autowired properties.

First, I created a properties component:

@ConfigurationProperties("app") @Component @Data
public class AppProperties {
    boolean failOnEmptyFileList = true;
    boolean exitWhenFinished = true;
}

...autowired the properties component into my runner:

@Service
public class Loader implements ApplicationRunner {

    private AppProperties properties;

    @Autowired
    public Loader(AppProperties properties) {
        this.properties = properties;
    }
    ...

...and, in the run I only assert'ed when that property is enabled, which is defaulted to true for normal application usage:

@Override
public void run(ApplicationArguments args) throws Exception {
    if (properties.isFailOnEmptyFileList()) {
        Assert.notEmpty(args.getNonOptionArgs(), "Pass at least one filename on the command line");
    }

    // ...do some loading of files and such

    if (properties.isExitWhenFinished()) {
        System.exit(0);
    }
}

With that, I can tweak those properties to execute in a unit test friendly manner:

@RunWith(SpringRunner.class)
@SpringBootTest(properties = {
        "app.failOnEmptyFileList=false",
        "app.exitWhenFinished=false"
})
public class InconsistentJsonApplicationTests {

    @Test
    public void contextLoads() {
    }

}

I needed the exitWhenFinished part since my particular runner normally calls System.exit(0) and exiting that way leaves the unit test in a semi-failed state.