Null pointer exception when testing a rest web service

I get a null pointer exception when trying to test a web service

My code:

@Path("/")
public class SubscriptionService {

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    @Path("/status/{subsId}")
    public Response getSubscriptionStatus(@PathParam("subsId") int subsId) {
        return Response.status(200).entity("subscription status for id: " + subsId).build();
    }
}

Test class:

public class TestService {

    private SubscriptionService service;

    @Test
    public void testGetSubscriptionStatus() {
        final Response response = service.getSubscriptionStatus(5);

        Assert.assertEquals(200, response.getStatus());
        Assert.assertEquals("subscription status for id: 5", response.getEntity());
    }
}

The error appears here: final Response response = service.getSubscriptionStatus(5);

Does anyone have any idea why I get this error? Please help with a solution.