chore: checkpoint before Python removal

vendor/utf8parse/tests/utf-8-demo.rs

@@ -0,0 +1,31 @@
+use utf8parse::{Parser, Receiver};
+
+static UTF8_DEMO: &[u8] = include_bytes!("UTF-8-demo.txt");
+
+#[derive(Debug, PartialEq)]
+struct StringWrapper(String);
+
+impl Receiver for StringWrapper {
+    fn codepoint(&mut self, c: char) {
+        self.0.push(c);
+    }
+
+    fn invalid_sequence(&mut self) {}
+}
+
+#[test]
+fn utf8parse_test() {
+    let mut parser = Parser::new();
+
+    // utf8parse implementation
+    let mut actual = StringWrapper(String::new());
+
+    for byte in UTF8_DEMO {
+        parser.advance(&mut actual, *byte)
+    }
+
+    // standard library implementation
+    let expected = String::from_utf8_lossy(UTF8_DEMO);
+
+    assert_eq!(actual.0, expected);
+}