Add integration test for CmarkError::UnexpectedEvent

tests/integrate/main.rs

@@ -2,6 +2,34 @@ mod display;
 mod fmt;
 mod spec;
 
+#[cfg(test)]
+mod fuzzed {
+    use pulldown_cmark::{Event, HeadingLevel, Tag, TagEnd};
+    use pulldown_cmark_to_cmark::{cmark, CmarkError};
+
+    #[test]
+    fn cmark_with_invalid_event_stream() {
+        let events = [
+            Event::Start(Tag::Heading {
+                level: HeadingLevel::H2,
+                id: None,
+                classes: vec![],
+                attrs: vec![],
+            }),
+            Event::Start(Tag::Heading {
+                level: HeadingLevel::H2,
+                id: None,
+                classes: vec![],
+                attrs: vec![],
+            }),
+            Event::Text(pulldown_cmark::CowStr::Borrowed("hello")),
+            Event::End(TagEnd::Heading(HeadingLevel::H2)),
+            Event::End(TagEnd::Heading(HeadingLevel::H2)),
+        ];
+        assert!(matches!(cmark(events.iter(), String::new()), Err(CmarkError::UnexpectedEvent)));
+    }
+}
+
 #[cfg(test)]
 mod calculate_code_block_token_count {
     use pulldown_cmark::{CodeBlockKind, CowStr, Event, Tag, TagEnd};