diff --git a/crates/ra_mbe/src/mbe_parser.rs b/crates/ra_mbe/src/mbe_parser.rs
index 933d5154d126..957571835dc8 100644
--- a/crates/ra_mbe/src/mbe_parser.rs
+++ b/crates/ra_mbe/src/mbe_parser.rs
@@ -69,46 +69,38 @@ mod tests {
     use crate::ast_to_token_tree;
 
     #[test]
-    fn test_invalid_parse() {
-        expect_err("invalid", "expected subtree");
-
-        is_valid("($i:ident) => ()");
-        is_valid("($($i:ident)*) => ($_)");
-        is_valid("($($true:ident)*) => ($true)");
-        is_valid("($($false:ident)*) => ($false)");
-
-        expect_err("$i:ident => ()", "expected subtree");
-        expect_err("($i:ident) ()", "expected `=`");
-        expect_err("($($i:ident)_) => ()", "invalid repeat");
+    fn test_valid_arms() {
+        fn check(macro_body: &str) {
+            let m = parse_macro_arm(macro_body);
+            m.unwrap();
+        }
 
-        expect_err("($i) => ($i)", "invalid macro definition");
-        expect_err("($i:) => ($i)", "invalid macro definition");
+        check("($i:ident) => ()");
+        check("($($i:ident)*) => ($_)");
+        check("($($true:ident)*) => ($true)");
+        check("($($false:ident)*) => ($false)");
     }
 
-    fn expect_err(macro_body: &str, expected: &str) {
-        assert_eq!(
-            create_rules(&format_macro(macro_body)),
-            Err(ParseError::Expected(String::from(expected)))
-        );
-    }
+    #[test]
+    fn test_invalid_arms() {
+        fn check(macro_body: &str, err: &str) {
+            let m = parse_macro_arm(macro_body);
+            assert_eq!(m, Err(ParseError::Expected(String::from(err))));
+        }
 
-    fn is_valid(macro_body: &str) {
-        assert!(create_rules(&format_macro(macro_body)).is_ok());
-    }
+        check("invalid", "expected subtree");
+
+        check("$i:ident => ()", "expected subtree");
+        check("($i:ident) ()", "expected `=`");
+        check("($($i:ident)_) => ()", "invalid repeat");
 
-    fn format_macro(macro_body: &str) -> String {
-        format!(
-            "
-        macro_rules! foo {{
-            {}
-        }}
-",
-            macro_body
-        )
+        check("($i) => ($i)", "invalid macro definition");
+        check("($i:) => ($i)", "invalid macro definition");
     }
 
-    fn create_rules(macro_definition: &str) -> Result<crate::MacroRules, ParseError> {
-        let source_file = ast::SourceFile::parse(macro_definition).ok().unwrap();
+    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::MacroCall::cast).unwrap();