+// The Touchable field signifies whether the Touch method will
+// succeed. Defaults to true. Note that Bad and Touchable are
+// independent: a MockVolume may be set up so that Put fails but Touch
+// works or vice versa.
+//
+// TODO(twp): rename Bad to something more descriptive, e.g. Writable,
+// and make sure that the tests that rely on it are testing the right
+// thing. We may need to simulate Writable, Touchable and Corrupt
+// volumes in different ways.
+//