Running DropwizardAppRule before each test in a class using junit

I have a test class that has several tests. At the moment I have this to start up the server, wipe the database etc:

@ClassRule
public static final DropwizardAppRule<ServiceConfig> RULE =
        new DropwizardAppRule<ServiceConfig>(ServiceApp.class, ResourceHelpers.resourceFilePath("config.yml"));

All my tests work with this individually. But when I run them all together some fail since other tests modify data. I tried doing the following but I'm getting null pointers when calling RULE.getPort():

@ClassRule
public static DropwizardAppRule<ServiceConfig> RULE;

@Before
public void beforeClass() {
     RULE = new DropwizardAppRule<ServiceConfig>(ServiceApp.class, ResourceHelpers.resourceFilePath("config.yml"));
}

I would have expected this to work but it doesn't seem to set the values of RULE properly. Any ideas?