Add test autocompletion for fish

#426

etc/fish/bloop.fish

@@ -57,6 +57,23 @@ function __fish_seen_subcommand_from_project_commands
     __fish_seen_subcommand_from $prj
 end
 
+# https://github.com/fish-shell/fish-shell/blob/04795eb8ea63e9b68bc85342aae81b9a60cd09c8/share/functions/__fish_prev_arg_in.fish
+function __fish_prev_arg_in
+    set -l tokens (commandline -co)
+    set -l tokenCount (count $tokens)
+    if test $tokenCount -lt 2
+        # need at least cmd and prev argument
+        return 1
+    end
+    for arg in $argv
+        if string match -q -- $tokens[-1] $argv[0]
+            return 0
+        end
+    end
+
+	return 1
+end
+
 function _flags_for_command -a cmd
     bloop autocomplete --format fish --mode flags --command $cmd
 end
@@ -82,6 +99,8 @@ complete -c bloop -f -n "__assert_args_count 0" -a '(_commands)'
 # Only a project command has been provided
 complete -c bloop -f -n "__assert_args_count 1; and __fish_seen_subcommand_from_project_commands" -a '(_projects)'
 
+# Only a project command has been provided
+complete -c bloop -x -n "__fish_seen_subcommand_from test; and not __fish_prev_arg_in --only" -a '(_testsfqcn)'
 
 for cmd in (_commands)
     set -l minTokens (_is_project_command $cmd)
@@ -98,4 +117,4 @@ for cmd in (_commands)
             _bloop_cmpl_ $minTokens $cmd -l $parsed[1]
         end
     end
-end
+end