Creates a noop test in "experimental" for internal purposes, plus a few tweaks...

Creates a noop test in "experimental" for internal purposes, plus a few tweaks and clarifications in the top-level README.md.

PiperOrigin-RevId: 347847486

tensorflow_federated/experimental/README.md

-This directory contains experimental code that is being incubated. Do not depend
-on this code from other parts of TFF, as it can change at any time. All code
-included here should retain private visibility while in the incubation stage.
+# TensorFlow Federated Experimental
+
+This directory contains experimental code that is being incubated and intended
+to be surfaced through the `tff.experimental` namespace while we evolve the API
+surface. Code quality, documentation, etc., are expected to be on par with the
+rest of the codebase during the incubation process. Do not depend on this code
+from other parts of TFF, as it can change at any time. All code included here
+should retain private visibility while in the incubation stage (except for
+what's necessary for inclusion in the `tff.experimental` API).

tensorflow_federated/experimental/python/BUILD

+package(default_visibility = ["//visibility:private"])
+
+licenses(["notice"])

tensorflow_federated/experimental/python/core/BUILD

+package(default_visibility = ["//visibility:private"])
+
+licenses(["notice"])

tensorflow_federated/experimental/python/core/api/BUILD

+load("@rules_python//python:defs.bzl", "py_test")
+
+package(default_visibility = ["//visibility:private"])
+
+licenses(["notice"])
+
+py_test(
+    name = "noop_test",
+    size = "small",
+    srcs = ["noop_test.py"],
+    python_version = "PY3",
+    srcs_version = "PY3",
+    tags = [
+        "nopresubmit",
+    ],
+)

tensorflow_federated/experimental/python/core/api/noop_test.py

+# Copyright 2020, The TensorFlow Federated Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Noop test to serve as a temporary placeholder until we have a real one."""
+
+from absl.testing import absltest
+
+
+class NoopTest(absltest.TestCase):
+
+  def test_nothing(self):
+    pass
+
+
+if __name__ == '__main__':
+  absltest.main()