func commonTestStateDriverReadStateAfterUpdate(t *testing.T, d core.StateDriver) {
	state := &testState{IntField: 1234, StrField: "testString"}
	key := "testKeyReadUpdate"

	err := d.WriteState(key, state, json.Marshal)
	if err != nil {
		t.Fatalf("failed to write state. Error: %s", err)
	}

	state.StrField = "testStringUpdated"
	err = d.WriteState(key, state, json.Marshal)
	if err != nil {
		t.Fatalf("failed to update state. Error: %s", err)
	}

	readState := &testState{}
	err = d.ReadState(key, readState, json.Unmarshal)
	if err != nil {
		t.Fatalf("failed to read state. Error: %s", err)
	}

	if readState.IntField != state.IntField || readState.StrField != state.StrField {
		t.Fatalf("Read state didn't match state written. Wrote: %v Read: %v",
			state, readState)
	}
}
func commonTestStateDriverWatchAllStateModify(t *testing.T, d core.StateDriver) {
	state := &testState{IntField: 1234, StrField: "testString"}
	modState := &testState{IntField: 5678, StrField: "modString"}
	baseKey := "modify"
	key := baseKey + "/testKeyWatchAll"

	err := d.WriteState(key, state, json.Marshal)
	if err != nil {
		t.Fatalf("failed to write state. Error: %s", err)
	}
	defer func() {
		d.ClearState(key)
	}()

	recvErr := make(chan error, 1)
	stateCh := make(chan core.WatchState, 1)
	timer := time.After(waitTimeout)

	go func(rsps chan core.WatchState, retErr chan error) {
		err := d.WatchAllState(baseKey, state, json.Unmarshal, stateCh)
		if err != nil {
			retErr <- err
			return
		}
	}(stateCh, recvErr)

	// trigger modify after a slight pause to ensure that events are not missed
	time.Sleep(time.Second)
	err = d.WriteState(key, modState, json.Marshal)
	if err != nil {
		t.Fatalf("failed to write state. Error: %s", err)
	}

for_label:
	for {
		select {
		case watchState := <-stateCh:
			s := watchState.Curr.(*testState)
			if s.IntField != modState.IntField || s.StrField != modState.StrField {
				t.Fatalf("Watch state mismatch. Expctd: %+v, Rcvd: %+v", modState, s)
			}
			if watchState.Prev == nil {
				t.Fatalf("Received a modify event without previous state value set.")
			}
			s = watchState.Prev.(*testState)
			if s.IntField != state.IntField || s.StrField != state.StrField {
				t.Fatalf("Watch state mismatch. Expctd: %+v, Rcvd: %+v", state, s)
			}
			break for_label
		case err := <-recvErr:
			t.Fatalf("Watch failed. Error: %s", err)
			break for_label
		case <-timer:
			t.Fatalf("timed out waiting for events")
			break for_label
		}
	}
}
func commonTestStateDriverWriteState(t *testing.T, d core.StateDriver) {
	state := &testState{IgnoredField: d, IntField: 1234,
		StrField: "testString"}
	key := "testKey"

	err := d.WriteState(key, state, json.Marshal)
	if err != nil {
		t.Fatalf("failed to write state. Error: %s", err)
	}
}
func commonTestStateDriverReadStateAfterClear(t *testing.T, d core.StateDriver) {
	state := &testState{IntField: 1234, StrField: "testString"}
	key := "testKeyReadClear"

	err := d.WriteState(key, state, json.Marshal)
	if err != nil {
		t.Fatalf("failed to write state. Error: %s", err)
	}

	err = d.ClearState(key)
	if err != nil {
		t.Fatalf("failed to clear state. Error: %s", err)
	}

	readState := &testState{}
	err = d.ReadState(key, readState, json.Unmarshal)
	if err == nil {
		t.Fatalf("Able to read cleared state!. Key: %s, Value: %v",
			key, readState)
	}
}