Finished the check_form_mistake function.

umbra/mistake_finder.py

@@ -123,9 +123,16 @@ class MistakeFinder:
         if last_shd_index < 0:
             src_index = 0
         else:
-            src_index = ### Hier verder
-            # Vergelijk alleen met het woord dat vlak voor het shadow woord
-            # voorkomt.
+            src_index = self._source.index(self._shadow[last_shd_index].source)
+        while self._source[src_index].get_difference(shd_word) > 0 and\
+                not form_mistake and src_index < len(self._source) - 1:
+            src_word = self._source[src_index]
+            form_mistake = self.form_related(src_word, shd_word)
+            if form_mistake:
+                shd_word.mistake = Mistake.FORM
+                shd_word.source = src_word
+                src_word.mistake = Mistake.FORM
+            src_index += 1
         return form_mistake
 
     def _check_repetition(self, word, index):