Make sure Sandy Device Plugins can be unit testsed

Summary: Add unit tests to verify that the unit test utilities for for Sandy device plugins work as expected. Fixed a bug revealed by that and cleaned up some TODO's

Reviewed By: jknoxville, passy, nikoant

Differential Revision: D22693928

fbshipit-source-id: 93162db19d826d0cd7f642cef1447fd756261ac8

desktop/flipper-plugin/src/__tests__/DeviceTestPlugin.tsx

@@ -0,0 +1,60 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import * as React from 'react';
+import {DevicePluginClient, Device} from '../plugin/DevicePlugin';
+import {usePlugin} from '../plugin/PluginContext';
+import {createState, useValue} from '../state/atom';
+
+export function supportsDevice(_device: Device) {
+  return true;
+}
+
+export function devicePlugin(client: DevicePluginClient) {
+  const logStub = jest.fn();
+  const activateStub = jest.fn();
+  const deactivateStub = jest.fn();
+  const destroyStub = jest.fn();
+  const state = createState(
+    {
+      count: 0,
+    },
+    {
+      persist: 'counter',
+    },
+  );
+
+  client.device.onLogEntry((entry) => {
+    state.update((d) => {
+      d.count++;
+    });
+    logStub(entry);
+  });
+  client.onActivate(activateStub);
+  client.onDeactivate(deactivateStub);
+  client.onDestroy(destroyStub);
+
+  return {
+    logStub,
+    activateStub,
+    deactivateStub,
+    destroyStub,
+    state,
+  };
+}
+
+export function Component() {
+  const api = usePlugin(devicePlugin);
+  const count = useValue(api.state).count;
+
+  // @ts-expect-error
+  api.bla;
+
+  return <h1>Hi from test plugin {count}</h1>;
+}