std: test a variety of ways to extend a Wtf8Buf

library/std/src/sys_common/wtf8/tests.rs

@@ -725,3 +725,27 @@ fn wtf8_utf8_boundary_between_surrogates() {
  string.push(CodePoint::from_u32(0xD800).unwrap());
  check_utf8_boundary(&string, 3);
 }
+
+#[test]
+fn wobbled_wtf8_plus_bytes_isnt_utf8() {
+ let mut string: Wtf8Buf = unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").to_owned() };
+ assert!(!string.is_known_utf8);
+ string.extend_from_slice(b"some utf-8");
+ assert!(!string.is_known_utf8);
+}
+
+#[test]
+fn wobbled_wtf8_plus_str_isnt_utf8() {
+ let mut string: Wtf8Buf = unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").to_owned() };
+ assert!(!string.is_known_utf8);
+ string.push_str("some utf-8");
+ assert!(!string.is_known_utf8);
+}
+
+#[test]
+fn unwobbly_wtf8_plus_utf8_is_utf8() {
+ let mut string: Wtf8Buf = Wtf8Buf::from_str("hello world");
+ assert!(string.is_known_utf8);
+ string.push_str("some utf-8");
+ assert!(string.is_known_utf8);
+}