protected final boolean isConnected() {
        return service != null;
    }
@Test
    void testIsConnected() {
        AbstractServiceConnectionManager<Object> connectionManager =
                new TestServiceConnectionManager();

        assertThat(connectionManager.isConnected()).isFalse();

        connectionManager.connect(new Object());
        assertThat(connectionManager.isConnected()).isTrue();

        connectionManager.disconnect();
        assertThat(connectionManager.isConnected()).isFalse();

        connectionManager.close();
        assertThat(connectionManager.isConnected()).isFalse();
    }