Add missing test (#911).

docs/how-to/backup-your-databases.md

@@ -466,13 +466,14 @@ exclude them. <span class="minilink minilink-addedin">Prior to version
 1.7.3</span>Special files were not auto-excluded, and you were responsible for
 excluding them yourself. Common directories to exclude are `/dev` and `/run`,
 but that may not be exhaustive.
-5. Database hooks also implicitly enable the `one_file_system` option, which
-means Borg won't cross filesystem boundaries when looking for files to backup.
-This is especially important when running borgmatic in a container, as
-container volumes are mounted as separate filesystems. One work-around is to
-explicitly add each mounted volume you'd like to backup to
+5. <span class="minilink minilink-addedin">Prior to version 1.8.15</span>
+Database hooks also implicitly enabled the `one_file_system` option, which
+meant Borg wouldn't cross filesystem boundaries when looking for files to
+backup. When borgmatic was running in a container, this often required a
+work-around to explicitly add each mounted backup volume to
 `source_directories` instead of relying on Borg to include them implicitly via
-a parent directory.
+a parent directory. However, as of borgmatic 1.8.15, `one_file_system` is no
+longer auto-enabled and such work-arounds aren't necessary.
 
 
 ### Manual restoration