Make sure that limited top-level exports are exposed from flipper-plugin

Summary: This prefixes APIs of `flipper-plugin`, that are used by Flipper, but should not be used by plugins directly, with `_`. Also added tests to make sure we are always intentional when extending the exposed APIs

Reviewed By: passy

Differential Revision: D24991700

fbshipit-source-id: ed3700efa188fca7f5a14d5c68250598cf011e42

desktop/flipper-plugin/src/__tests__/api.node.tsx

@@ -0,0 +1,53 @@
+/**
+ * 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 FlipperPluginModule from '../index';
+
+test('Correct top level API exposed', () => {
+  const exposedAPIs: string[] = [];
+  const exposedTypes: string[] = [];
+  Object.entries(FlipperPluginModule).forEach(([key, value]) => {
+    if (key[0] === '_') {
+      return;
+    }
+    if (value === undefined) {
+      exposedTypes.push(key);
+    } else {
+      exposedAPIs.push(key);
+    }
+  });
+  expect(exposedAPIs.sort()).toMatchInlineSnapshot(`
+    Array [
+      "Layout",
+      "NUX",
+      "TestUtils",
+      "createState",
+      "renderReactRoot",
+      "theme",
+      "usePlugin",
+      "useValue",
+    ]
+  `);
+  expect(exposedTypes.sort()).toMatchInlineSnapshot(`
+    Array [
+      "Atom",
+      "DefaultKeyboardAction",
+      "Device",
+      "DeviceLogEntry",
+      "DeviceLogListener",
+      "DevicePluginClient",
+      "DeviceType",
+      "FlipperLib",
+      "LogLevel",
+      "MenuEntry",
+      "NormalizedMenuEntry",
+      "PluginClient",
+    ]
+  `);
+});