test: add alternate example of issue, without definition

Author: ChristianMurphy

tests/fuzz.rs

@@ -127,9 +127,24 @@ fn fuzz() -> Result<(), String> {
         ),
         Ok("<p>&lt;</p>".to_string()),
         "12: mdx: handle invalid mdx without panic (GH-26)"
+    )
+    
+    assert_eq!(
         to_html("[:]:a\n-\na\n-"),
         "<h2>-\na</h2>",
         "10: handle link in heading"
+    )
+
+    assert_eq!(
+        to_html("[:]:a\n-\na\n-"),
+        "<h2>-\na</h2>",
+        "xx: handle link in heading (GH-22)"
+    );
+
+    assert_eq!(
+        to_html("a\n-\n--\na\n-"),
+        "<h2>a</h2>\n<h2>--\na</h2>",
+        "xx: two setext headings next to each other (GH-22)"
     );
 
     Ok(())