Add a quick check of our cast validation.

src/syntax/validate.rs

@@ -158,3 +158,19 @@ impl Expression {
         }
     }
 }
+
+#[test]
+fn cast_checks_are_reasonable() {
+    let good_stmt = Statement::parse(0, "x = <u16>4u8;").expect("valid test case");
+    let (good_errs, good_warns) = good_stmt.validate(&mut HashMap::new());
+
+    assert!(good_errs.is_empty());
+    assert!(good_warns.is_empty());
+
+    let bad_stmt = Statement::parse(0, "x = <apple>4u8;").expect("valid test case");
+    let (bad_errs, bad_warns) = bad_stmt.validate(&mut HashMap::new());
+
+    assert!(bad_warns.is_empty());
+    assert_eq!(bad_errs.len(), 1);
+    assert!(matches!(bad_errs[0], Error::UnknownType(_, ref x) if x == "apple"));
+}