Add loop test

src/parser.rs

@@ -377,7 +377,19 @@ else
         )];
         assert_eq!(deelang_parser::program(prgm).unwrap(), expected);
     }
-
+    #[test]
+    fn test_loop() {
+	let prgm = r"loop until i > 100 a";
+	let expected = vec![Stmt::Loop(Loop::Until(GuardedBlock {
+	    guard: Expr::Relop(
+		">".to_string(),
+		Box::new(Expr::Id("i".to_string())),
+		Box::new(Expr::Atom(Atom::Num(100.0))),
+	    ),
+	    block: vec![Stmt::BareExpr(Expr::Id("a".to_string()))],
+	}))];
+	assert_eq!(deelang_parser::program(prgm).unwrap(), expected);
+    }
     #[test]
     fn test_preprocess() {
         let prgm = r"