Add Setup and Extending top level navs

Summary: Distinguish between integrating flipper, and developing plugins.

Reviewed By: passy

Differential Revision: D15148448

fbshipit-source-id: 7c772fa1cea7d5ed789a984039afc37bc0b8a927

docs/extending/testing.md

@@ -0,0 +1,95 @@
+---
+id: testing
+title: Testing
+---
+
+Developer tools are only used if they work. We have built APIs to test plugins.
+
+## Android
+
+Start by creating your first test file in this directory `MyFlipperPluginTest.java`. In the test method body we create our plugin which we want to test as well as a `FlipperConnectionMock`. In this contrived example we simply assert that our plugin's connected status is what we expect.
+
+```java
+@RunWith(RobolectricTestRunner.class)
+public class MyFlipperPluginTest {
+
+  @Test
+  public void myTest() {
+    final MyFlipperPlugin plugin = new MyFlipperPlugin();
+    final FlipperConnectionMock connection = new FlipperConnectionMock();
+
+    plugin.onConnect(connection);
+    assertThat(plugin.connected(), equalTo(true));
+  }
+}
+```
+
+There are two mock classes that are used to construct tests `FlipperConnectionMock` and `FlipperResponderMock`. Together these can be used to write very powerful tests to verify the end to end behavior of your plugin. For example we can test if for a given incoming message our plugin responds as we expect.
+
+```java
+@Test
+public void myTest() {
+  final MyFlipperPlugin plugin = new MyFlipperPlugin();
+  final FlipperConnectionMock connection = new FlipperConnectionMock();
+  final FlipperResponderMock responder = new FlipperResponderMock();
+
+  plugin.onConnect(connection);
+
+  final FlipperObject params = new FlipperObject.Builder()
+      .put("phrase", "flipper")
+      .build();
+  connection.receivers.get("myMethod").onReceive(params, responder);
+
+  assertThat(responder.successes, hasItem(
+      new FlipperObject.Builder()
+          .put("phrase", "ranos")
+          .build()));
+}
+```
+
+## C++
+
+Start by creating your first test file in this directory `MyFlipperPluginTests.cpp` and import the testing utilities from `fbsource//xplat/sonar/xplat:FlipperTestLib`. These utilities mock out core pieces of the communication channel so that you can test your plugin in isolation.
+
+```
+#include <MyFlipperPlugin/MyFlipperPlugin.h>
+#include <FlipperTestLib/FlipperConnectionMock.h>
+#include <FlipperTestLib/FlipperResponderMock.h>
+
+#include <folly/json.h>
+#include <gtest/gtest.h>
+
+namespace facebook {
+namespace flipper {
+namespace test {
+
+TEST(MyFlipperPluginTests, testDummy) {
+  EXPECT_EQ(1 + 1, 2);
+}
+
+} // namespace test
+} // namespace flipper
+} // namespace facebook
+```
+
+Here is a simple test using these mock utilities to create a plugin, send some data, and assert that the result is as expected.
+
+```
+TEST(MyFlipperPluginTests, testDummy) {
+  std::vector<folly::dynamic> successfulResponses;
+  auto responder = std::make_unique<FlipperResponderMock>(&successfulResponses);
+  auto conn = std::make_shared<FlipperConnectionMock>();
+
+  MyFlipperPlugin plugin;
+  plugin.didConnect(conn);
+
+  folly::dynamic message = folly::dynamic::object("param1", "hello");
+  folly::dynamic expectedResponse = folly::dynamic::object("response", "Hi there");
+
+  auto receiver = conn->receivers_["someMethod"];
+  receiver(message, std::move(responder));
+
+  EXPECT_EQ(successfulResponses.size(), 1);
+  EXPECT_EQ(successfulResponses.back(), expectedResponse);
+}
+```