Add formatter demo test

Author: knutwannheden

rewrite/tests/python/all/format/demo_test.py

@@ -0,0 +1,23 @@
+from typing import Optional
+
+from rewrite.java import Space, P
+from rewrite.python import PythonVisitor
+from rewrite.test import rewrite_run, python, from_visitor
+
+
+def test_remove_all_spaces_demo():
+    rewrite_run(
+        python(
+            # language=python
+            """
+            class Foo:
+                def getter(self, row):
+                    pass
+            """, """classFoo:defgetter(self,row):pass"""
+        ),
+        recipe=from_visitor(NoSpaces())
+    )
+
+class NoSpaces(PythonVisitor):
+    def visit_space(self, space: Optional[Space], loc: Optional[Space.Location], p: P) -> Optional[Space]:
+        return Space.EMPTY if space else None