Get the unicode grapheme seg tests passing on screen, with minimal modification

We ignore tests including ACII control codes and we modify the results
when there are grapheme breaks before zero width characters.

kitty_tests/datatypes.py

@@ -640,7 +640,41 @@ class TestDataTypes(BaseTest):
     def test_split_into_graphemes(self):
         self.assertEqual(char_props_for('\ue000')['category'], 'Co')
         self.ae(split_into_graphemes('ab'), ['a', 'b'])
+        s = self.create_screen(cols=12)
+        excluded_chars = set(range(32))
+
+        def is_excluded(text):
+            return bool(set(map(ord, text)) & excluded_chars)
+
+        def adapt_cell_text(cells):
+            for cell in cells:
+                gp = split_into_graphemes(cell)
+                if len(gp) == 1:
+                    yield cell
+                else:
+                    for i, g in enumerate(gp[:-1]):
+                        if wcswidth(gp[i+1][0]) != 0:
+                            raise AssertionError(
+                                f'cell {cell!r} contains grapheme break point at non zero width character for Test #{i}: {test["comment"]}')
+                    yield from gp
+
         for i, test in enumerate(json.loads(read_kitty_resource('GraphemeBreakTest.json', __name__.rpartition('.')[0]))):
             expected = test['data']
-            actual = split_into_graphemes(''.join(expected))
+            text = ''.join(expected)
+            actual = split_into_graphemes(text)
             self.ae(expected, actual, f'Test #{i} failed: {test["comment"]}')
+            if is_excluded(text):
+                continue
+            s.carriage_return(), s.erase_in_line()
+            s.draw(' ' + text)
+            actual = []
+            for x in range(s.cursor.x):
+                cell = s.cpu_cells(0, x)
+                if cell['x'] > 0:
+                    continue
+                ct = cell['text']
+                if x == 0:
+                    ct = ct[1:]
+                if ct:
+                    actual.append(ct)
+            self.ae(expected, list(adapt_cell_text(actual)), f'Test #{i} failed: {test["comment"]}')