add more tests for unicode range edge cases

tests/unicode-range.rs

@@ -16,3 +16,27 @@ test!(
     "a {\n  color: U+45????;\n}\n",
     "a {\n  color: U+45????;\n}\n"
 );
+test!(
+    lowercase_u,
+    "a {\n  color: u+27a;\n}\n",
+    "a {\n  color: u+27a;\n}\n"
+);
+error!(
+    interpolated_range,
+    "a {\n  color: U+2A#{70}C;\n}\n", "Error: Expected end of identifier."
+);
+error!(
+    unicode_escape_within_range,
+    "a {\n  color: U+B\\a;\n}\n", "Error: Expected end of identifier."
+);
+error!(
+    longer_than_6_characters,
+    "a {\n  color: U+1234567;\n}\n", "Error: Expected end of identifier."
+);
+// I believe this to be a bug in the dart-sass implementation
+// we test for it to ensure full parity
+test!(
+    length_of_6_with_question_mark,
+    "a {\n  color: U+123456?;\n}\n",
+    "a {\n  color: U+123456?;\n}\n"
+);