test(policy): add roundtrip test for semantic Display

Author: febyeji

src/policy/semantic.rs

@@ -1057,6 +1057,31 @@ mod tests {
         assert!(StringPolicy::from_str("# {pk(A), pk(B), pk(C)} = 2").is_err());
     }
 
+    fn roundtrip(s: &str) {
+        let policy = StringPolicy::from_str(s).unwrap();
+        assert_eq!(StringPolicy::from_str(&policy.to_string()).unwrap(), policy);
+    }
+
+    #[test]
+    fn display_roundtrip() {
+        roundtrip("TRIVIAL");
+        roundtrip("UNSATISFIABLE");
+        roundtrip("pk(A)");
+        roundtrip("after(100)");
+        roundtrip("older(50)");
+        roundtrip("(pk(A) ∧ pk(B))");
+        roundtrip("(pk(A) ∨ pk(B))");
+        roundtrip("(pk(A) ∧ pk(B) ∧ pk(C))");
+        roundtrip("(pk(A) ∨ pk(B) ∨ pk(C))");
+        roundtrip("((pk(A) ∧ pk(B)) ∨ pk(C))");
+        roundtrip("#{pk(A), pk(B), pk(C)} = 2");
+        roundtrip("(pk(A) ∧ #{pk(B), pk(C), pk(D)} = 2)");
+        // Display always emits the mathematical form, so feeding it the
+        // function-call form exercises the parser → Display → parser path.
+        roundtrip("or(and(pk(A),pk(B)),pk(C))");
+        roundtrip("thresh(2,pk(A),pk(B),pk(C))");
+    }
+
     #[test]
     fn semantic_analysis() {
         let policy = StringPolicy::from_str("pk()").unwrap();