Bottom line: Spotify has been reluctant to offer a blacklisting feature on its platform but is apparently giving in to overwhelming demand. Sometimes, a company knows what's best and other times, the ideal course of action is listening (no pun intended) to users.
Spotify is testing a heavily requested feature that allows users to block artists they don't want to hear from.
According to Thurrott's Mehedi Hassan, a member of Spotify's beta program on iOS, blocking an artist will prevent their music from playing through personal libraries and playlists, curated playlists, radios, charts and anywhere else. You aren't even able to manually play their music without unblocking them first.
The blacklist feature doesn't apply to tracks in which the artist is featured, however, so it's possible that you might still hear a verse or two from a banned artist on occasion if they are a guest on another artist's song.
The block feature can be accessed via the "..." menu on an artist's page; simply tap "Don't play this artist" to do the deed.
As of yesterday, Spotify's official stance on the matter was that it's not possible to block an artist.
Hassan notes that access to the feature seems limited to a small number of iOS users right now, adding that the program was recently expanded, perhaps as recently as last week. Hassan wasn't able to find evidence of testing on other platforms like desktop and the web.