Improve unit test robustness

Summary: When running tests locally, some are quite flaky, and there is a lot of error logging noise. This diff doesn't remove all of it, but does reduce it significantly.

Reviewed By: nikoant

Differential Revision: D20034619

fbshipit-source-id: 183f74475b644f803b2f92b1b1301f4d0f6e193a

src/dispatcher/__tests__/TestPlugin.js

@@ -12,3 +12,8 @@ import {FlipperPlugin} from 'flipper';
 export default class extends FlipperPlugin {
   static id = 'Static ID';
 }
+
+test('TestPlugin', () => {
+  // supress jest warning
+  expect(true).toBeTruthy();
+});