Add in memory filesystem clearing

Change-Id: Ibd22eddeec87f660e729099f702f52cdd6b828ea

taskflow/persistence/backends/impl_memory.py

@@ -114,6 +114,10 @@ class FakeFilesystem(object):
         """Return list of all children of the given path."""
         return [node.item for node in self._fetch_node(path)]
 
+    def clear(self):
+        for node in list(self._root.reverse_iter()):
+            node.disassociate()
+
     def _iter_pieces(self, path, include_root=False):
         if path == self._root.item:
             # Check for this directly as the following doesn't work with

taskflow/tests/unit/persistence/test_memory_persistence.py

@@ -84,6 +84,17 @@ class MemoryFilesystemTest(test.TestCase):
                 path += "/" + p
             self.assertIsNone(fs[path])
 
+    def test_clear(self):
+        fs = impl_memory.FakeFilesystem()
+        paths = ['/b', '/c', '/a/b/c']
+        for p in paths:
+            fs.ensure_path(p)
+        for p in paths:
+            self.assertIsNone(self._get_item_path(fs, p))
+        fs.clear()
+        for p in paths:
+            self.assertRaises(exc.NotFound, self._get_item_path, fs, p)
+
     def test_not_found(self):
         fs = impl_memory.FakeFilesystem()
         self.assertRaises(exc.NotFound, self._get_item_path, fs, '/c')