Added unit test for negative number literals in macros.

crates/mbe/src/subtree_source.rs

@@ -202,3 +202,24 @@ fn convert_leaf(leaf: &tt::Leaf) -> TtToken {
         tt::Leaf::Punct(punct) => convert_punct(*punct),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::{convert_literal, TtToken};
+    use syntax::{SmolStr, SyntaxKind};
+
+    #[test]
+    fn test_negative_literal() {
+        assert_eq!(
+            convert_literal(&tt::Literal {
+                id: tt::TokenId::unspecified(),
+                text: SmolStr::new("-42.0")
+            }),
+            TtToken {
+                kind: SyntaxKind::FLOAT_NUMBER,
+                is_joint_to_next: false,
+                text: SmolStr::new("-42.0")
+            }
+        );
+    }
+}