Is it possible to designate an alternative wifi connection test site? I live in mainland China and uses a Google Pixel bought from Hong Kong. Current system version is 7.1.2. As you might know, Google servers are not accessible in China without the use of VPNs and such. So whenever I connect to a wifi network, my phone tries to connect to Google connection test server, but does not do that via ShadowSocksR (my VPN app) so the test always fails and the phone tells me the wifi has no internet connection, which isn't the case and isn't very helpful either.

So I am wondering, is it possible to designate an alternative connection test site that is accessible within mainland China? I know the one Windows 10 uses (http://www.msftconnecttest.com/redirect) is usable so is there any way I can let my Pixel use it by default?
Yes. Since Android 7.1 the method is a little different (not gonna mention the old method here) - fire up adb shell then use the command settings put global captive_portal_https_url **site domain here**.

In the past g.cn (Google's remaining Chinese domain) worked alright, but since Nougat for better reliability I'm using one hosted by V2EX: captive.v2ex.co/generate_204, so the full command becomes settings put global captive_portal_https_url https://captive.v2ex.co/generate_204.