If you have an inactive World of Warcraft account and you don't already own Battle for Azeroth, you may want to check your BattleNet launcher to see if you've been selected for a special 3-day trial of the latest expansion. Players will run through a tutorial after choosing a class to play and having it "boosted" to 110. After that, players can try out the Fight for Lordaeron, obtain the Heart of Azeroth necklace and progress through the game.
It appears, however, that progress is not saved for those who purchase BfA. The fine print reads, "While your 3-day trial phase is active you can re-play the trial experience with up to 11 additional characters. Once your trial is complete, you can purchase Battle for Azeroth, which includes a level 110 Character Boost to unlock the character of your choice."
Read the details on the World of Warcraft Battle for Azeroth promotion page.