Recently, in the latest community update, when a user asked if a test server is coming the next season, Activision replied that they are planning to have it between Season 7 and 8.
It will probably be a public beta test build, and players will be able to download it using the links given by Activision.
We can expect a lot of content related to COD Mobile's second anniversary, which is on 1st October. However, there will be limited slots for both the Android and iOS players, so it is suggested that you download the COD Mobile Season 8 test server as soon as it gets released.
To avoid any issues while installing the beta test build, make sure you have at least 6 GB of free space in your device. The registrations for the COD Mobile Chinese version's beta test server will begin from 23rd August, so we could expect the global one in the next week or so.
COD Mobile Season 8 will be based on the anniversary theme and will feature a bunch of events, modes, rewards, etc.
Meanwhile, Activision has confirmed the addition of Scrapyard and Monastery maps in COD Mobile Season 7. In addition to this, Hades and Crossbow weapons are also confirmed to arrive.