Add test for failing StreamBlock validation

wagtail/wagtailcore/tests/test_blocks.py

@@ -1239,6 +1239,38 @@ class TestStreamBlock(unittest.TestCase):
             html
         )
 
+    def test_validation_errors(self):
+        class ValidatedBlock(blocks.StreamBlock):
+            char = blocks.CharBlock()
+            url = blocks.URLBlock()
+        block = ValidatedBlock()
+
+        value = [
+            blocks.BoundBlock(
+                block=block.child_blocks['char'],
+                value='',
+            ),
+            blocks.BoundBlock(
+                block=block.child_blocks['char'],
+                value='foo',
+            ),
+            blocks.BoundBlock(
+                block=block.child_blocks['url'],
+                value='http://example.com/',
+            ),
+            blocks.BoundBlock(
+                block=block.child_blocks['url'],
+                value='not a url',
+            ),
+        ]
+
+        with self.assertRaises(ValidationError) as catcher:
+            block.clean(value)
+        self.assertEqual(catcher.exception.params, {
+            0: ['This field is required.'],
+            3: ['Enter a valid URL.'],
+        })
+
     def test_html_declarations(self):
         class ArticleBlock(blocks.StreamBlock):
             heading = blocks.CharBlock()