Fix failing tests in czruby functions

fn/czruby_purge

@@ -9,12 +9,17 @@ czruby_purge() {
     return 1
   fi
 
-  # Store current default ruby
-  default_ruby="$(greadlink -f "$czruby_datadir/default" 2>/dev/null)"
+  # Store current default ruby (use readlink on Linux, greadlink on macOS)
+  if command -v greadlink &>/dev/null; then
+    default_ruby="$(greadlink -f "$czruby_datadir/default" 2>/dev/null)"
+  else
+    default_ruby="$(readlink -f "$czruby_datadir/default" 2>/dev/null)"
+  fi
   default_ruby="${default_ruby:t}"
 
   # Process each file in czruby_datadir
-  for file in "$czruby_datadir"/*; do
+  # Use (N) glob qualifier to handle empty directory without error
+  for file in "$czruby_datadir"/*(N); do
     [[ -f "$file" ]] || continue
     key="${file:t}"
 
@@ -44,10 +49,14 @@ czruby_purge() {
       rm "$file"
       ((purged++))
 
-      # If this was the default, remove the default symlink
+      # If this was the default, reset to system
       if [[ "$key" == "$default_ruby" ]]; then
-        rm "$czruby_datadir/default"
-        czruby_set_default system
+        rm -f "$czruby_datadir/default"
+        RUBIES_DEFAULT="system"
+        # Create symlink to system config if it exists
+        if [[ -f "$czruby_datadir/system" ]]; then
+          ln -fs "$czruby_datadir/system" "$czruby_datadir/default"
+        fi
       fi
     fi
   done

fn/czruby_reset

@@ -6,13 +6,23 @@
 	local ruby_root="${2:-$RUBY_ROOT}"
 	local excludes=()
 
-	# TODO consider replacing loop
-	for place in "$gem_path"; do
+	# Remove old RUBY_ROOT/bin from path
+	if [[ -n "$RUBY_ROOT" ]]; then
+		excludes+=("$RUBY_ROOT/bin")
+	fi
+
+	# Remove old GEM_HOME/bin from path
+	if [[ -n "$GEM_HOME" ]]; then
+		excludes+=("$GEM_HOME/bin")
+	fi
+
+	# Remove all gem_path bin directories from path
+	for place in $gem_path; do
 		local bin="$place/bin"
-		excludes=("$bin" "${excludes[@]}")  # Append to the array correctly
+		excludes+=("$bin")
 	done
 
-	if [[ $#gem_path > 0 ]]; then
+	if [[ ${#excludes[@]} -gt 0 ]]; then
 		# remove any excluded paths
 		path=(${path:|excludes})
 	fi

fn/czruby_set_default

@@ -1,7 +1,8 @@
 # Sets the default Ruby environment to use when no specific version is specified.
 {
+	# Check for empty argument before applying default
+	[[ -z "$1" ]] && return 1
 	local choice="${1:-system}"
-	[[ -z $choice ]] && return 1
 	if [[ -z ${(M)rubies:#*$choice} ]]; then
 		print "That ruby is not available\n\n"
 		czruby