Errors are now displayed on attach so use control mode to test

instead.

regress/if-shell-error.sh

@@ -11,16 +11,13 @@ TMUX="$TEST_TMUX -Ltest"
 $TMUX kill-server 2>/dev/null
 
 TMP=$(mktemp)
-trap "rm -f $TMP" 0 1 15
+OUT=$(mktemp)
+trap "rm -f $TMP $OUT" 0 1 15
 
 cat <<EOF >$TMP
 if 'true' 'wibble wobble'
 EOF
 
-$TMUX -f$TMP new -d || exit 1
-sleep 1
-E=$($TMUX display -p '#{pane_in_mode}')
-$TMUX kill-server 2>/dev/null
-[ "$E" = "1" ] || exit 1
-
-exit 0
+$TMUX -f$TMP -C new <<EOF >$OUT
+EOF
+grep -q "^%config-error $TMP:1: $TMP:1: unknown command: wibble$" $OUT