public ClientTpcConfig setConnectionCount(int connectionCount) {
        this.connectionCount = checkNotNegative(connectionCount, "connectionCount");
        return this;
    }
@Test
    public void test_setConnectionCount_whenNegative() {
        ClientTpcConfig config = new ClientTpcConfig();
        assertThrows(IllegalArgumentException.class, () -> config.setConnectionCount(-1));
    }