Improve tests for Path methods

Replicates graphql/graphql-js@f42cee9

Author: Cito

tests/pyutils/test_path.py

@@ -2,27 +2,23 @@
 
 
 def describe_path():
-    def add_path():
-        path = Path(None, 0, None)
-        assert path.prev is None
-        assert path.key == 0
-        prev, path = path, Path(path, 1, None)
-        assert path.prev is prev
-        assert path.key == 1
-        prev, path = path, Path(path, "two", None)
-        assert path.prev is prev
-        assert path.key == "two"
+    def can_create_a_path():
+        first = Path(None, 1, "First")
+        assert first.prev is None
+        assert first.key == 1
+        assert first.typename == "First"
 
-    def add_key():
-        prev = Path(None, 0, None)
-        path = prev.add_key("one")
-        assert path.prev is prev
-        assert path.key == "one"
+    def can_add_a_new_key_to_an_existing_path():
+        first = Path(None, 1, "First")
+        second = first.add_key("two", "Second")
+        assert second.prev is first
+        assert second.key == "two"
+        assert second.typename == "Second"
 
-    def as_list():
-        path = Path(None, 1, None)
-        assert path.as_list() == [1]
-        path = path.add_key("two")
-        assert path.as_list() == [1, "two"]
-        path = path.add_key(3)
-        assert path.as_list() == [1, "two", 3]
+    def can_convert_a_path_to_a_list_of_its_keys():
+        root = Path(None, 0, "Root")
+        assert root.as_list() == [0]
+        first = root.add_key("one", "First")
+        assert first.as_list() == [0, "one"]
+        second = first.add_key(2, "Second")
+        assert second.as_list() == [0, "one", 2]