map-keys() returns a comma separated list

src/builtin/map.rs

@@ -2,7 +2,7 @@ use std::collections::HashMap;
 
 use super::Builtin;
 use crate::common::{Brackets, ListSeparator};
-use crate::value::{Value, SassMap};
+use crate::value::{SassMap, Value};
 
 pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
     f.insert(
@@ -42,7 +42,7 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
             };
             Ok(Value::List(
                 map.keys(),
-                ListSeparator::Space,
+                ListSeparator::Comma,
                 Brackets::None,
             ))
         }),

tests/map.rs

@@ -35,6 +35,16 @@ test!(
     "a {\n  color: map-keys((a: b));\n}\n",
     "a {\n  color: a;\n}\n"
 );
+test!(
+    map_keys_are_comma_separated,
+    "a {\n  color: map-keys((a: b, c: d));\n}\n",
+    "a {\n  color: a, c;\n}\n"
+);
+test!(
+    map_keys_empty,
+    "a {\n  color: inspect(map-keys(()));\n}\n",
+    "a {\n  color: ();\n}\n"
+);
 error!(
     map_keys_non_map,
     "a {\n  color: map-keys(foo);\n}\n", "Error: $map: foo is not a map."