1 files changed, 45 insertions, 0 deletions

diff --git a/crates/mbe/src/tests/rule.rs b/crates/mbe/src/tests/rule.rs
new file mode 100644
index 000000000..07277966d
--- /dev/null
+++ b/crates/mbe/src/tests/rule.rs
@@ -0,0 +1,45 @@
+use syntax::{ast, AstNode};
+
+use crate::ast_to_token_tree;
+
+use super::*;
+
+#[test]
+fn test_valid_arms() {
+    fn check(macro_body: &str) {
+        let m = parse_macro_arm(macro_body);
+        m.unwrap();
+    }
+
+    check("($i:ident) => ()");
+    check("($($i:ident)*) => ($_)");
+    check("($($true:ident)*) => ($true)");
+    check("($($false:ident)*) => ($false)");
+    check("($) => ($)");
+}
+
+#[test]
+fn test_invalid_arms() {
+    fn check(macro_body: &str, err: ParseError) {
+        let m = parse_macro_arm(macro_body);
+        assert_eq!(m, Err(err));
+    }
+    check("invalid", ParseError::Expected("expected subtree".into()));
+
+    check("$i:ident => ()", ParseError::Expected("expected subtree".into()));
+    check("($i:ident) ()", ParseError::Expected("expected `=`".into()));
+    check("($($i:ident)_) => ()", ParseError::InvalidRepeat);
+
+    check("($i) => ($i)", ParseError::UnexpectedToken("bad fragment specifier 1".into()));
+    check("($i:) => ($i)", ParseError::UnexpectedToken("bad fragment specifier 1".into()));
+}
+
+fn parse_macro_arm(arm_definition: &str) -> Result<crate::MacroRules, ParseError> {
+    let macro_definition = format!(" macro_rules! m {{ {} }} ", arm_definition);
+    let source_file = ast::SourceFile::parse(&macro_definition).ok().unwrap();
+    let macro_definition =
+        source_file.syntax().descendants().find_map(ast::MacroRules::cast).unwrap();
+
+    let (definition_tt, _) = ast_to_token_tree(&macro_definition.token_tree().unwrap()).unwrap();
+    crate::MacroRules::parse(&definition_tt)
+}