Dropwizard application integration test, DropwizardAppRule port is null - dropwizard

Question

I am fairly new to Dropwzard so feel free to guide me incase I am not doing something right. Here is my scenario.
I am writing an integration test for the whole application (Which runs okay) following a tutorial from a book. However my test runs but not the full app on the specified port. Below is my test
import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Entity;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import org.glassfish.jersey.client.authentication.HttpAuthenticationFeature;
import org.junit.Before;
import org.junit.ClassRule;
import org.junit.Test;
import demo.basicapi.configuration.BasicConfiguration;
import demo.basicapi.domain.Contact;
import io.dropwizard.testing.junit.DropwizardAppRule;
import junit.framework.TestCase;
public class AppTest extends TestCase {
private Client client;
private Contact dummyClient = new Contact(0, "Jane", "Doe", "[phone]");
#ClassRule
public static final DropwizardAppRule<BasicConfiguration> RULE = new DropwizardAppRule<BasicConfiguration>(
App.class, "config.yaml");
#Before
public void setUp() {
client = ClientBuilder.newBuilder().build();
// Set the credentials to be used by the client
HttpAuthenticationFeature feature = HttpAuthenticationFeature.basic("admin", "password");
client.register(feature);
}
#Test
public void testcreateAndRetrieveContact() {
// Create a new contact by performing the appropriate http request (POST)
WebTarget target = client.target(String.format("http://localhost:%d/contact", RULE.getLocalPort()));
Response response = target.request(MediaType.APPLICATION_JSON)
.post(Entity.entity(dummyClient, MediaType.APPLICATION_JSON));
// Check that the response has the appropriate response code (201)
assertEquals(response.getStatus(), 201);
}
}
However when I run the test, I get a Null pointer exception when retrieving the port number
RULE.getLocalPort() // This returns null in my test.
Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.274 sec <<< FAILURE!
testcreateAndRetrieveContact(demo.basicapi.AppTest) Time elapsed: 0.132 sec <<< ERROR!
java.lang.NullPointerException
at java.base/java.util.Objects.requireNonNull(Objects.java:221)
at io.dropwizard.testing.DropwizardTestSupport.getLocalPort(DropwizardTestSupport.java:249)
at io.dropwizard.testing.junit.DropwizardAppRule.getLocalPort(DropwizardAppRule.java:180)
at demo.basicapi.AppTest.testcreateAndRetrieveContact(AppTest.java:41)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
Also, I am a bit concerned that if I play around with this line, I dont get any error whatsoever, It doesn't matter the name of config file,
#ClassRule
public static final DropwizardAppRule<BasicConfiguration> RULE = new DropwizardAppRule<BasicConfiguration>(
App.class, "config.yaml");
Changing the name of the .yaml file to something nonexisted does not throw any other error in the tests.
I am using Dropwizard version 1.3.12, Is there anything I could change to be succesful. I for now I am not focussing on separate representation tests, but feel free to advise. Thanks.
<dependency>
<groupId>io.dropwizard</groupId>
<artifactId>dropwizard-testing</artifactId>
<version>1.3.12</version>
</dependency>
<dependency>
<groupId>org.hamcrest</groupId>
<artifactId>hamcrest-all</artifactId>
<version>1.3</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.10</version>
<scope>test</scope>
</dependency>