Add option to jest to run tests only locally, or on linux (#2609)

Summary:
Pull Request resolved: https://github.com/facebook/flipper/pull/2609

Make it possible to mark some tests to run on non-CI, or unix only

Reviewed By: nikoant

Differential Revision: D29813506

fbshipit-source-id: 140f8a4eaed5af3282ab9d139b46a52818be0934

desktop/types/jest-extensions.d.ts

@@ -0,0 +1,22 @@
+/**
+ * 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
+ */
+
+declare namespace jest {
+  interface It {
+    /**
+     * This test will not be executed on Github / SandCastle,
+     * since, for example, it relies on precise timer reliability
+     */
+    local: jest.It;
+    /**
+     * This test will only run on non-windows machines
+     */
+    unix: jest.It;
+  }
+}