@Test
    void testStartStop() throws Exception {
        final Server server = ServerTest.server.server();
        assertThat(server.activePorts()).hasSize(1);
        server.stop().get();
        assertThat(server.activePorts()).isEmpty();
    }
Ensures that the {@link Server} is always started when a test begins. This is necessary even if we
enabled auto-start for {@link ServerRule} because we stop it in {@link #testStartStop()}.
core/src/test/java/com/linecorp/armeria/server/ServerTest.java