Add assignment parsing

src/compiler/parser/tests.rs

@@ -150,6 +150,12 @@ fn test_assignment_chain() {
     );
 }
 
+#[test]
+#[should_panic]
+fn test_assignment_invalid() {
+    parse(&tokenize("a ="));
+}
+
 #[test]
 fn test_unary_basic() {
     let result = parse(&tokenize("not x"));