import io.micronaut.runtime.Micronaut
class Application {
    static void main(String... args) {
        Micronaut.run Application.class
    }
}

To run the application from a unit test you can use the interface:

import io.micronaut.context.annotation.Property;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.runtime.server.EmbeddedServer;
import io.micronaut.test.annotation.MicronautTest;
import org.junit.jupiter.api.Test;
import javax.inject.Inject;
import static org.junit.jupiter.api.Assertions.assertEquals;
    @Inject
    EmbeddedServer server; (1)
    @Inject
    @Client("/")
    HttpClient client; (2)
    @Test
    void testHelloWorldResponse() {
        String response = client.toBlocking() (3)
                .retrieve(HttpRequest.GET("/hello"));
        assertEquals("Hello World", response); //) (4)
    }
}

import io.micronaut.context.annotation.Property
import io.micronaut.http.client.HttpClient
import io.micronaut.http.client.annotation.Client
import io.micronaut.runtime.server.EmbeddedServer
import io.micronaut.test.annotation.MicronautTest
import org.junit.jupiter.api.Test
import javax.inject.Inject
@MicronautTest
class HelloControllerSpec {
    @Inject
    lateinit var server: EmbeddedServer (1)
    @Inject
    @field:Client("/")
    lateinit var client: HttpClient (2)
    @Test
    fun testHelloWorldResponse() {
        val rsp: String = client.toBlocking() (3)
                .retrieve("/hello")
        assertEquals("Hello World", rsp) (4)
    }
}