tests/test_block.py: test append after block

tests/test_block.py

@@ -32,3 +32,7 @@ def test_assign_after_block():
     'It is an error to assign to a block key after the block.'
     with pytest.raises(ParseError):
         loads_xbc('a { a = 1 }\na = 1')
+
+def test_append_after_block():
+    'Modifying keys after a block is legal.'
+    loads_xbc('a\na { b = 1 }\na += 1') == {'a': '1', 'a.b': '1'}