Update tests to compile again.

src/parser/org_source.rs

@@ -45,7 +45,7 @@ impl<'s> OrgSource<'s> {
     }
 
     pub fn get_preceding_character(&self) -> Option<char> {
-        todo!()
+        self.preceding_character
     }
 
     pub fn is_at_start_of_line(&self) -> bool {
@@ -357,4 +357,12 @@ mod tests {
         assert_eq!(input.slice(6..).is_at_start_of_line(), true);
         assert_eq!(input.slice(6..).slice(10..).is_at_start_of_line(), false);
     }
+
+    #[test]
+    fn preceding_character_unicode() {
+        let input = OrgSource::new("🧡💛💚💙💜");
+        assert_eq!(input.get_preceding_character(), None);
+        assert_eq!(input.slice(8..).get_preceding_character(), Some('💛'));
+    }
+
 }