Copy WTF-8 code into core/alloc (for better diffs)

1 files changed, 751 insertions, 0 deletions

diff --git a/library/alloc/src/wtf8/tests.rs b/library/alloc/src/wtf8/tests.rs
new file mode 100644
index 00000000000..b57c99a8452
--- /dev/null
+++ b/library/alloc/src/wtf8/tests.rs
@@ -0,0 +1,751 @@
+use super::*;
+
+#[test]
+fn code_point_from_u32() {
+    assert!(CodePoint::from_u32(0).is_some());
+    assert!(CodePoint::from_u32(0xD800).is_some());
+    assert!(CodePoint::from_u32(0x10FFFF).is_some());
+    assert!(CodePoint::from_u32(0x110000).is_none());
+}
+
+#[test]
+fn code_point_to_u32() {
+    fn c(value: u32) -> CodePoint {
+        CodePoint::from_u32(value).unwrap()
+    }
+    assert_eq!(c(0).to_u32(), 0);
+    assert_eq!(c(0xD800).to_u32(), 0xD800);
+    assert_eq!(c(0x10FFFF).to_u32(), 0x10FFFF);
+}
+
+#[test]
+fn code_point_to_lead_surrogate() {
+    fn c(value: u32) -> CodePoint {
+        CodePoint::from_u32(value).unwrap()
+    }
+    assert_eq!(c(0).to_lead_surrogate(), None);
+    assert_eq!(c(0xE9).to_lead_surrogate(), None);
+    assert_eq!(c(0xD800).to_lead_surrogate(), Some(0xD800));
+    assert_eq!(c(0xDBFF).to_lead_surrogate(), Some(0xDBFF));
+    assert_eq!(c(0xDC00).to_lead_surrogate(), None);
+    assert_eq!(c(0xDFFF).to_lead_surrogate(), None);
+    assert_eq!(c(0x1F4A9).to_lead_surrogate(), None);
+    assert_eq!(c(0x10FFFF).to_lead_surrogate(), None);
+}
+
+#[test]
+fn code_point_to_trail_surrogate() {
+    fn c(value: u32) -> CodePoint {
+        CodePoint::from_u32(value).unwrap()
+    }
+    assert_eq!(c(0).to_trail_surrogate(), None);
+    assert_eq!(c(0xE9).to_trail_surrogate(), None);
+    assert_eq!(c(0xD800).to_trail_surrogate(), None);
+    assert_eq!(c(0xDBFF).to_trail_surrogate(), None);
+    assert_eq!(c(0xDC00).to_trail_surrogate(), Some(0xDC00));
+    assert_eq!(c(0xDFFF).to_trail_surrogate(), Some(0xDFFF));
+    assert_eq!(c(0x1F4A9).to_trail_surrogate(), None);
+    assert_eq!(c(0x10FFFF).to_trail_surrogate(), None);
+}
+
+#[test]
+fn code_point_from_char() {
+    assert_eq!(CodePoint::from_char('a').to_u32(), 0x61);
+    assert_eq!(CodePoint::from_char('💩').to_u32(), 0x1F4A9);
+}
+
+#[test]
+fn code_point_to_string() {
+    assert_eq!(format!("{:?}", CodePoint::from_char('a')), "U+0061");
+    assert_eq!(format!("{:?}", CodePoint::from_char('💩')), "U+1F4A9");
+}
+
+#[test]
+fn code_point_to_char() {
+    fn c(value: u32) -> CodePoint {
+        CodePoint::from_u32(value).unwrap()
+    }
+    assert_eq!(c(0x61).to_char(), Some('a'));
+    assert_eq!(c(0x1F4A9).to_char(), Some('💩'));
+    assert_eq!(c(0xD800).to_char(), None);
+}
+
+#[test]
+fn code_point_to_char_lossy() {
+    fn c(value: u32) -> CodePoint {
+        CodePoint::from_u32(value).unwrap()
+    }
+    assert_eq!(c(0x61).to_char_lossy(), 'a');
+    assert_eq!(c(0x1F4A9).to_char_lossy(), '💩');
+    assert_eq!(c(0xD800).to_char_lossy(), '\u{FFFD}');
+}
+
+#[test]
+fn wtf8buf_new() {
+    assert_eq!(Wtf8Buf::new().bytes, b"");
+}
+
+#[test]
+fn wtf8buf_from_str() {
+    assert_eq!(Wtf8Buf::from_str("").bytes, b"");
+    assert_eq!(Wtf8Buf::from_str("aé 💩").bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+}
+
+#[test]
+fn wtf8buf_from_string() {
+    assert_eq!(Wtf8Buf::from_string(String::from("")).bytes, b"");
+    assert_eq!(Wtf8Buf::from_string(String::from("aé 💩")).bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+}
+
+#[test]
+fn wtf8buf_from_wide() {
+    let buf = Wtf8Buf::from_wide(&[]);
+    assert_eq!(buf.bytes, b"");
+    assert!(buf.is_known_utf8);
+
+    let buf = Wtf8Buf::from_wide(&[0x61, 0xE9, 0x20, 0xD83D, 0xDCA9]);
+    assert_eq!(buf.bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+    assert!(buf.is_known_utf8);
+
+    let buf = Wtf8Buf::from_wide(&[0x61, 0xE9, 0x20, 0xD83D, 0xD83D, 0xDCA9]);
+    assert_eq!(buf.bytes, b"a\xC3\xA9 \xED\xA0\xBD\xF0\x9F\x92\xA9");
+    assert!(!buf.is_known_utf8);
+
+    let buf = Wtf8Buf::from_wide(&[0xD800]);
+    assert_eq!(buf.bytes, b"\xED\xA0\x80");
+    assert!(!buf.is_known_utf8);
+
+    let buf = Wtf8Buf::from_wide(&[0xDBFF]);
+    assert_eq!(buf.bytes, b"\xED\xAF\xBF");
+    assert!(!buf.is_known_utf8);
+
+    let buf = Wtf8Buf::from_wide(&[0xDC00]);
+    assert_eq!(buf.bytes, b"\xED\xB0\x80");
+    assert!(!buf.is_known_utf8);
+
+    let buf = Wtf8Buf::from_wide(&[0xDFFF]);
+    assert_eq!(buf.bytes, b"\xED\xBF\xBF");
+    assert!(!buf.is_known_utf8);
+}
+
+#[test]
+fn wtf8buf_push_str() {
+    let mut string = Wtf8Buf::new();
+    assert_eq!(string.bytes, b"");
+    assert!(string.is_known_utf8);
+
+    string.push_str("aé 💩");
+    assert_eq!(string.bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+    assert!(string.is_known_utf8);
+}
+
+#[test]
+fn wtf8buf_push_char() {
+    let mut string = Wtf8Buf::from_str("aé ");
+    assert_eq!(string.bytes, b"a\xC3\xA9 ");
+    assert!(string.is_known_utf8);
+
+    string.push_char('💩');
+    assert_eq!(string.bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+    assert!(string.is_known_utf8);
+}
+
+#[test]
+fn wtf8buf_push() {
+    let mut string = Wtf8Buf::from_str("aé ");
+    assert_eq!(string.bytes, b"a\xC3\xA9 ");
+    assert!(string.is_known_utf8);
+
+    string.push(CodePoint::from_char('💩'));
+    assert_eq!(string.bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+    assert!(string.is_known_utf8);
+
+    fn c(value: u32) -> CodePoint {
+        CodePoint::from_u32(value).unwrap()
+    }
+
+    let mut string = Wtf8Buf::new();
+    string.push(c(0xD83D)); // lead
+    assert!(!string.is_known_utf8);
+    string.push(c(0xDCA9)); // trail
+    assert_eq!(string.bytes, b"\xF0\x9F\x92\xA9"); // Magic!
+
+    let mut string = Wtf8Buf::new();
+    string.push(c(0xD83D)); // lead
+    assert!(!string.is_known_utf8);
+    string.push(c(0x20)); // not surrogate
+    string.push(c(0xDCA9)); // trail
+    assert_eq!(string.bytes, b"\xED\xA0\xBD \xED\xB2\xA9");
+
+    let mut string = Wtf8Buf::new();
+    string.push(c(0xD800)); // lead
+    assert!(!string.is_known_utf8);
+    string.push(c(0xDBFF)); // lead
+    assert_eq!(string.bytes, b"\xED\xA0\x80\xED\xAF\xBF");
+
+    let mut string = Wtf8Buf::new();
+    string.push(c(0xD800)); // lead
+    assert!(!string.is_known_utf8);
+    string.push(c(0xE000)); // not surrogate
+    assert_eq!(string.bytes, b"\xED\xA0\x80\xEE\x80\x80");
+
+    let mut string = Wtf8Buf::new();
+    string.push(c(0xD7FF)); // not surrogate
+    assert!(string.is_known_utf8);
+    string.push(c(0xDC00)); // trail
+    assert!(!string.is_known_utf8);
+    assert_eq!(string.bytes, b"\xED\x9F\xBF\xED\xB0\x80");
+
+    let mut string = Wtf8Buf::new();
+    string.push(c(0x61)); // not surrogate, < 3 bytes
+    assert!(string.is_known_utf8);
+    string.push(c(0xDC00)); // trail
+    assert!(!string.is_known_utf8);
+    assert_eq!(string.bytes, b"\x61\xED\xB0\x80");
+
+    let mut string = Wtf8Buf::new();
+    string.push(c(0xDC00)); // trail
+    assert!(!string.is_known_utf8);
+    assert_eq!(string.bytes, b"\xED\xB0\x80");
+}
+
+#[test]
+fn wtf8buf_push_wtf8() {
+    let mut string = Wtf8Buf::from_str("aé");
+    assert_eq!(string.bytes, b"a\xC3\xA9");
+    string.push_wtf8(Wtf8::from_str(" 💩"));
+    assert_eq!(string.bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+    assert!(string.is_known_utf8);
+
+    fn w(v: &[u8]) -> &Wtf8 {
+        unsafe { Wtf8::from_bytes_unchecked(v) }
+    }
+
+    let mut string = Wtf8Buf::new();
+    string.push_wtf8(w(b"\xED\xA0\xBD")); // lead
+    string.push_wtf8(w(b"\xED\xB2\xA9")); // trail
+    assert_eq!(string.bytes, b"\xF0\x9F\x92\xA9"); // Magic!
+
+    let mut string = Wtf8Buf::new();
+    string.push_wtf8(w(b"\xED\xA0\xBD")); // lead
+    string.push_wtf8(w(b" ")); // not surrogate
+    string.push_wtf8(w(b"\xED\xB2\xA9")); // trail
+    assert_eq!(string.bytes, b"\xED\xA0\xBD \xED\xB2\xA9");
+    assert!(!string.is_known_utf8);
+
+    let mut string = Wtf8Buf::new();
+    string.push_wtf8(w(b"\xED\xA0\x80")); // lead
+    string.push_wtf8(w(b"\xED\xAF\xBF")); // lead
+    assert_eq!(string.bytes, b"\xED\xA0\x80\xED\xAF\xBF");
+    assert!(!string.is_known_utf8);
+
+    let mut string = Wtf8Buf::new();
+    string.push_wtf8(w(b"\xED\xA0\x80")); // lead
+    string.push_wtf8(w(b"\xEE\x80\x80")); // not surrogate
+    assert_eq!(string.bytes, b"\xED\xA0\x80\xEE\x80\x80");
+    assert!(!string.is_known_utf8);
+
+    let mut string = Wtf8Buf::new();
+    string.push_wtf8(w(b"\xED\x9F\xBF")); // not surrogate
+    string.push_wtf8(w(b"\xED\xB0\x80")); // trail
+    assert_eq!(string.bytes, b"\xED\x9F\xBF\xED\xB0\x80");
+    assert!(!string.is_known_utf8);
+
+    let mut string = Wtf8Buf::new();
+    string.push_wtf8(w(b"a")); // not surrogate, < 3 bytes
+    string.push_wtf8(w(b"\xED\xB0\x80")); // trail
+    assert_eq!(string.bytes, b"\x61\xED\xB0\x80");
+    assert!(!string.is_known_utf8);
+
+    let mut string = Wtf8Buf::new();
+    string.push_wtf8(w(b"\xED\xB0\x80")); // trail
+    assert_eq!(string.bytes, b"\xED\xB0\x80");
+    assert!(!string.is_known_utf8);
+}
+
+#[test]
+fn wtf8buf_truncate() {
+    let mut string = Wtf8Buf::from_str("aé");
+    assert!(string.is_known_utf8);
+
+    string.truncate(3);
+    assert_eq!(string.bytes, b"a\xC3\xA9");
+    assert!(string.is_known_utf8);
+
+    string.truncate(1);
+    assert_eq!(string.bytes, b"a");
+    assert!(string.is_known_utf8);
+
+    string.truncate(0);
+    assert_eq!(string.bytes, b"");
+    assert!(string.is_known_utf8);
+}
+
+#[test]
+fn wtf8buf_truncate_around_non_bmp() {
+    let mut string = Wtf8Buf::from_str("💩");
+    assert!(string.is_known_utf8);
+
+    string.truncate(4);
+    assert_eq!(string.bytes, b"\xF0\x9F\x92\xA9");
+    assert!(string.is_known_utf8);
+
+    string.truncate(0);
+    assert_eq!(string.bytes, b"");
+    assert!(string.is_known_utf8);
+}
+
+#[test]
+#[should_panic]
+fn wtf8buf_truncate_fail_code_point_boundary() {
+    let mut string = Wtf8Buf::from_str("aé");
+    string.truncate(2);
+}
+
+#[test]
+#[should_panic]
+fn wtf8buf_truncate_fail_longer() {
+    let mut string = Wtf8Buf::from_str("aé");
+    string.truncate(4);
+}
+
+#[test]
+#[should_panic]
+fn wtf8buf_truncate_splitting_non_bmp3() {
+    let mut string = Wtf8Buf::from_str("💩");
+    assert!(string.is_known_utf8);
+    string.truncate(3);
+}
+
+#[test]
+#[should_panic]
+fn wtf8buf_truncate_splitting_non_bmp2() {
+    let mut string = Wtf8Buf::from_str("💩");
+    assert!(string.is_known_utf8);
+    string.truncate(2);
+}
+
+#[test]
+#[should_panic]
+fn wtf8buf_truncate_splitting_non_bmp1() {
+    let mut string = Wtf8Buf::from_str("💩");
+    assert!(string.is_known_utf8);
+    string.truncate(1);
+}
+
+#[test]
+fn wtf8buf_into_string() {
+    let mut string = Wtf8Buf::from_str("aé 💩");
+    assert!(string.is_known_utf8);
+    assert_eq!(string.clone().into_string(), Ok(String::from("aé 💩")));
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    assert!(!string.is_known_utf8);
+    assert_eq!(string.clone().into_string(), Err(string));
+}
+
+#[test]
+fn wtf8buf_into_string_lossy() {
+    let mut string = Wtf8Buf::from_str("aé 💩");
+    assert_eq!(string.clone().into_string_lossy(), String::from("aé 💩"));
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    assert_eq!(string.clone().into_string_lossy(), String::from("aé 💩�"));
+}
+
+#[test]
+fn wtf8buf_from_iterator() {
+    fn f(values: &[u32]) -> Wtf8Buf {
+        values.iter().map(|&c| CodePoint::from_u32(c).unwrap()).collect::<Wtf8Buf>()
+    }
+    assert_eq!(
+        f(&[0x61, 0xE9, 0x20, 0x1F4A9]),
+        Wtf8Buf { bytes: b"a\xC3\xA9 \xF0\x9F\x92\xA9".to_vec(), is_known_utf8: true }
+    );
+
+    assert_eq!(f(&[0xD83D, 0xDCA9]).bytes, b"\xF0\x9F\x92\xA9"); // Magic!
+    assert_eq!(
+        f(&[0xD83D, 0x20, 0xDCA9]),
+        Wtf8Buf { bytes: b"\xED\xA0\xBD \xED\xB2\xA9".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        f(&[0xD800, 0xDBFF]),
+        Wtf8Buf { bytes: b"\xED\xA0\x80\xED\xAF\xBF".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        f(&[0xD800, 0xE000]),
+        Wtf8Buf { bytes: b"\xED\xA0\x80\xEE\x80\x80".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        f(&[0xD7FF, 0xDC00]),
+        Wtf8Buf { bytes: b"\xED\x9F\xBF\xED\xB0\x80".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        f(&[0x61, 0xDC00]),
+        Wtf8Buf { bytes: b"\x61\xED\xB0\x80".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(f(&[0xDC00]), Wtf8Buf { bytes: b"\xED\xB0\x80".to_vec(), is_known_utf8: false });
+}
+
+#[test]
+fn wtf8buf_extend() {
+    fn e(initial: &[u32], extended: &[u32]) -> Wtf8Buf {
+        fn c(value: &u32) -> CodePoint {
+            CodePoint::from_u32(*value).unwrap()
+        }
+        let mut string = initial.iter().map(c).collect::<Wtf8Buf>();
+        string.extend(extended.iter().map(c));
+        string
+    }
+
+    assert_eq!(
+        e(&[0x61, 0xE9], &[0x20, 0x1F4A9]),
+        Wtf8Buf { bytes: b"a\xC3\xA9 \xF0\x9F\x92\xA9".to_vec(), is_known_utf8: true }
+    );
+
+    assert_eq!(e(&[0xD83D], &[0xDCA9]).bytes, b"\xF0\x9F\x92\xA9"); // Magic!
+    assert_eq!(
+        e(&[0xD83D, 0x20], &[0xDCA9]),
+        Wtf8Buf { bytes: b"\xED\xA0\xBD \xED\xB2\xA9".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        e(&[0xD800], &[0xDBFF]),
+        Wtf8Buf { bytes: b"\xED\xA0\x80\xED\xAF\xBF".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        e(&[0xD800], &[0xE000]),
+        Wtf8Buf { bytes: b"\xED\xA0\x80\xEE\x80\x80".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        e(&[0xD7FF], &[0xDC00]),
+        Wtf8Buf { bytes: b"\xED\x9F\xBF\xED\xB0\x80".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        e(&[0x61], &[0xDC00]),
+        Wtf8Buf { bytes: b"\x61\xED\xB0\x80".to_vec(), is_known_utf8: false }
+    );
+    assert_eq!(
+        e(&[], &[0xDC00]),
+        Wtf8Buf { bytes: b"\xED\xB0\x80".to_vec(), is_known_utf8: false }
+    );
+}
+
+#[test]
+fn wtf8buf_show() {
+    let mut string = Wtf8Buf::from_str("a\té \u{7f}💩\r");
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    assert_eq!(format!("{string:?}"), "\"a\\té \\u{7f}\u{1f4a9}\\r\\u{d800}\"");
+}
+
+#[test]
+fn wtf8buf_as_slice() {
+    assert_eq!(Wtf8Buf::from_str("aé").as_slice(), Wtf8::from_str("aé"));
+}
+
+#[test]
+fn wtf8buf_show_str() {
+    let text = "a\té 💩\r";
+    let string = Wtf8Buf::from_str(text);
+    assert_eq!(format!("{text:?}"), format!("{string:?}"));
+}
+
+#[test]
+fn wtf8_from_str() {
+    assert_eq!(&Wtf8::from_str("").bytes, b"");
+    assert_eq!(&Wtf8::from_str("aé 💩").bytes, b"a\xC3\xA9 \xF0\x9F\x92\xA9");
+}
+
+#[test]
+fn wtf8_len() {
+    assert_eq!(Wtf8::from_str("").len(), 0);
+    assert_eq!(Wtf8::from_str("aé 💩").len(), 8);
+}
+
+#[test]
+fn wtf8_slice() {
+    assert_eq!(&Wtf8::from_str("aé 💩")[1..4].bytes, b"\xC3\xA9 ");
+}
+
+#[test]
+#[should_panic]
+fn wtf8_slice_not_code_point_boundary() {
+    let _ = &Wtf8::from_str("aé 💩")[2..4];
+}
+
+#[test]
+fn wtf8_slice_from() {
+    assert_eq!(&Wtf8::from_str("aé 💩")[1..].bytes, b"\xC3\xA9 \xF0\x9F\x92\xA9");
+}
+
+#[test]
+#[should_panic]
+fn wtf8_slice_from_not_code_point_boundary() {
+    let _ = &Wtf8::from_str("aé 💩")[2..];
+}
+
+#[test]
+fn wtf8_slice_to() {
+    assert_eq!(&Wtf8::from_str("aé 💩")[..4].bytes, b"a\xC3\xA9 ");
+}
+
+#[test]
+#[should_panic]
+fn wtf8_slice_to_not_code_point_boundary() {
+    let _ = &Wtf8::from_str("aé 💩")[5..];
+}
+
+#[test]
+fn wtf8_ascii_byte_at() {
+    let slice = Wtf8::from_str("aé 💩");
+    assert_eq!(slice.ascii_byte_at(0), b'a');
+    assert_eq!(slice.ascii_byte_at(1), b'\xFF');
+    assert_eq!(slice.ascii_byte_at(2), b'\xFF');
+    assert_eq!(slice.ascii_byte_at(3), b' ');
+    assert_eq!(slice.ascii_byte_at(4), b'\xFF');
+}
+
+#[test]
+fn wtf8_code_points() {
+    fn c(value: u32) -> CodePoint {
+        CodePoint::from_u32(value).unwrap()
+    }
+    fn cp(string: &Wtf8Buf) -> Vec<Option<char>> {
+        string.code_points().map(|c| c.to_char()).collect::<Vec<_>>()
+    }
+    let mut string = Wtf8Buf::from_str("é ");
+    assert_eq!(cp(&string), [Some('é'), Some(' ')]);
+    string.push(c(0xD83D));
+    assert_eq!(cp(&string), [Some('é'), Some(' '), None]);
+    string.push(c(0xDCA9));
+    assert_eq!(cp(&string), [Some('é'), Some(' '), Some('💩')]);
+}
+
+#[test]
+fn wtf8_as_str() {
+    assert_eq!(Wtf8::from_str("").as_str(), Ok(""));
+    assert_eq!(Wtf8::from_str("aé 💩").as_str(), Ok("aé 💩"));
+    let mut string = Wtf8Buf::new();
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    assert!(string.as_str().is_err());
+}
+
+#[test]
+fn wtf8_to_string_lossy() {
+    assert_eq!(Wtf8::from_str("").to_string_lossy(), Cow::Borrowed(""));
+    assert_eq!(Wtf8::from_str("aé 💩").to_string_lossy(), Cow::Borrowed("aé 💩"));
+    let mut string = Wtf8Buf::from_str("aé 💩");
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    let expected: Cow<'_, str> = Cow::Owned(String::from("aé 💩�"));
+    assert_eq!(string.to_string_lossy(), expected);
+}
+
+#[test]
+fn wtf8_display() {
+    fn d(b: &[u8]) -> String {
+        (&unsafe { Wtf8::from_bytes_unchecked(b) }).to_string()
+    }
+
+    assert_eq!("", d("".as_bytes()));
+    assert_eq!("aé 💩", d("aé 💩".as_bytes()));
+
+    let mut string = Wtf8Buf::from_str("aé 💩");
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    assert_eq!("aé 💩�", d(string.as_inner()));
+}
+
+#[test]
+fn wtf8_encode_wide() {
+    let mut string = Wtf8Buf::from_str("aé ");
+    string.push(CodePoint::from_u32(0xD83D).unwrap());
+    string.push_char('💩');
+    assert_eq!(
+        string.encode_wide().collect::<Vec<_>>(),
+        vec![0x61, 0xE9, 0x20, 0xD83D, 0xD83D, 0xDCA9]
+    );
+}
+
+#[test]
+fn wtf8_encode_wide_size_hint() {
+    let string = Wtf8Buf::from_str("\u{12345}");
+    let mut iter = string.encode_wide();
+    assert_eq!((1, Some(8)), iter.size_hint());
+    iter.next().unwrap();
+    assert_eq!((1, Some(1)), iter.size_hint());
+    iter.next().unwrap();
+    assert_eq!((0, Some(0)), iter.size_hint());
+    assert!(iter.next().is_none());
+}
+
+#[test]
+fn wtf8_clone_into() {
+    let mut string = Wtf8Buf::new();
+    Wtf8::from_str("green").clone_into(&mut string);
+    assert_eq!(string.bytes, b"green");
+
+    let mut string = Wtf8Buf::from_str("green");
+    Wtf8::from_str("").clone_into(&mut string);
+    assert_eq!(string.bytes, b"");
+
+    let mut string = Wtf8Buf::from_str("red");
+    Wtf8::from_str("green").clone_into(&mut string);
+    assert_eq!(string.bytes, b"green");
+
+    let mut string = Wtf8Buf::from_str("green");
+    Wtf8::from_str("red").clone_into(&mut string);
+    assert_eq!(string.bytes, b"red");
+
+    let mut string = Wtf8Buf::from_str("green");
+    assert!(string.is_known_utf8);
+    unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").clone_into(&mut string) };
+    assert_eq!(string.bytes, b"\xED\xA0\x80");
+    assert!(!string.is_known_utf8);
+}
+
+#[test]
+fn wtf8_to_ascii_lowercase() {
+    let lowercase = Wtf8::from_str("").to_ascii_lowercase();
+    assert_eq!(lowercase.bytes, b"");
+
+    let lowercase = Wtf8::from_str("GrEeN gRaPeS! 🍇").to_ascii_lowercase();
+    assert_eq!(lowercase.bytes, b"green grapes! \xf0\x9f\x8d\x87");
+
+    let lowercase = unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").to_ascii_lowercase() };
+    assert_eq!(lowercase.bytes, b"\xED\xA0\x80");
+    assert!(!lowercase.is_known_utf8);
+}
+
+#[test]
+fn wtf8_to_ascii_uppercase() {
+    let uppercase = Wtf8::from_str("").to_ascii_uppercase();
+    assert_eq!(uppercase.bytes, b"");
+
+    let uppercase = Wtf8::from_str("GrEeN gRaPeS! 🍇").to_ascii_uppercase();
+    assert_eq!(uppercase.bytes, b"GREEN GRAPES! \xf0\x9f\x8d\x87");
+
+    let uppercase = unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").to_ascii_uppercase() };
+    assert_eq!(uppercase.bytes, b"\xED\xA0\x80");
+    assert!(!uppercase.is_known_utf8);
+}
+
+#[test]
+fn wtf8_make_ascii_lowercase() {
+    let mut lowercase = Wtf8Buf::from_str("");
+    lowercase.make_ascii_lowercase();
+    assert_eq!(lowercase.bytes, b"");
+
+    let mut lowercase = Wtf8Buf::from_str("GrEeN gRaPeS! 🍇");
+    lowercase.make_ascii_lowercase();
+    assert_eq!(lowercase.bytes, b"green grapes! \xf0\x9f\x8d\x87");
+
+    let mut lowercase = unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").to_owned() };
+    lowercase.make_ascii_lowercase();
+    assert_eq!(lowercase.bytes, b"\xED\xA0\x80");
+    assert!(!lowercase.is_known_utf8);
+}
+
+#[test]
+fn wtf8_make_ascii_uppercase() {
+    let mut uppercase = Wtf8Buf::from_str("");
+    uppercase.make_ascii_uppercase();
+    assert_eq!(uppercase.bytes, b"");
+
+    let mut uppercase = Wtf8Buf::from_str("GrEeN gRaPeS! 🍇");
+    uppercase.make_ascii_uppercase();
+    assert_eq!(uppercase.bytes, b"GREEN GRAPES! \xf0\x9f\x8d\x87");
+
+    let mut uppercase = unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").to_owned() };
+    uppercase.make_ascii_uppercase();
+    assert_eq!(uppercase.bytes, b"\xED\xA0\x80");
+    assert!(!uppercase.is_known_utf8);
+}
+
+#[test]
+fn wtf8_to_owned() {
+    let string = unsafe { Wtf8::from_bytes_unchecked(b"\xED\xA0\x80").to_owned() };
+    assert_eq!(string.bytes, b"\xED\xA0\x80");
+    assert!(!string.is_known_utf8);
+}
+
+#[test]
+fn wtf8_valid_utf8_boundaries() {
+    let mut string = Wtf8Buf::from_str("aé 💩");
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    check_utf8_boundary(&string, 0);
+    check_utf8_boundary(&string, 1);
+    check_utf8_boundary(&string, 3);
+    check_utf8_boundary(&string, 4);
+    check_utf8_boundary(&string, 8);
+    check_utf8_boundary(&string, 14);
+    assert_eq!(string.len(), 14);
+
+    string.push_char('a');
+    check_utf8_boundary(&string, 14);
+    check_utf8_boundary(&string, 15);
+
+    let mut string = Wtf8Buf::from_str("a");
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    check_utf8_boundary(&string, 1);
+
+    let mut string = Wtf8Buf::from_str("\u{D7FF}");
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    check_utf8_boundary(&string, 3);
+
+    let mut string = Wtf8Buf::new();
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    string.push_char('\u{D7FF}');
+    check_utf8_boundary(&string, 3);
+}
+
+#[test]
+#[should_panic(expected = "byte index 4 is out of bounds")]
+fn wtf8_utf8_boundary_out_of_bounds() {
+    let string = Wtf8::from_str("aé");
+    check_utf8_boundary(&string, 4);
+}
+
+#[test]
+#[should_panic(expected = "byte index 1 is not a codepoint boundary")]
+fn wtf8_utf8_boundary_inside_codepoint() {
+    let string = Wtf8::from_str("é");
+    check_utf8_boundary(&string, 1);
+}
+
+#[test]
+#[should_panic(expected = "byte index 1 is not a codepoint boundary")]
+fn wtf8_utf8_boundary_inside_surrogate() {
+    let mut string = Wtf8Buf::new();
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    check_utf8_boundary(&string, 1);
+}
+
+#[test]
+#[should_panic(expected = "byte index 3 lies between surrogate codepoints")]
+fn wtf8_utf8_boundary_between_surrogates() {
+    let mut string = Wtf8Buf::new();
+    string.push(CodePoint::from_u32(0xD800).unwrap());
+    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);
+}