add breaking change for FlutterMain.setIsRunningInRobolectricTest removal (flutter#4561)

Author: xster

src/docs/release/breaking-changes/android-setIsRunningInRobolectricTest-removed.md

@@ -0,0 +1,73 @@
+---
+title: FlutterMain.setIsRunningInRobolectricTest on Android removed
+description: The test-only FlutterMain.setIsRunningInRobolectricTest API on the Android engine is consolidated into the FlutterInjector.
+---
+
+## Summary
+
+If you write Java JUnit tests (such as Robolectric tests) against the Flutter
+engine's Java embedding and used the
+`FlutterMain.setIsRunningInRobolectricTest(true)` API, replace it with
+
+```java
+FlutterJNI mockFlutterJNI = mock(FlutterJNI.class);
+FlutterInjector.setInstance(
+        new FlutterInjector.Builder()
+            .setFlutterLoader(new FlutterLoader(mockFlutterJNI))
+            .build());
+```
+
+This should be very uncommon.
+
+## Context
+
+The `FlutterMain` class itself is being deprecated and replaced with the
+`FlutterInjector` class. The `FlutterMain` class uses a number of
+static variables and functions than make it difficult to test.
+`FlutterMain.setIsRunningInRobolectricTest()` is one ad-hoc static
+mechanism to allow tests to run on the host machine on JVM without
+loading the libflutter.so native library (which can't be done on the host
+machine).
+
+Rather than one-off solutions, all dependency injections needed for tests
+in Flutter's Android/Java engine embedding are now moved to the
+[`FlutterInjector`](https://cs.opensource.google/flutter/engine/+/master:shell/platform/android/io/flutter/FlutterInjector.java)
+class.
+
+Within the `FlutterInjector` class, the `setFlutterLoader()` Builder
+function allows for control of how the [`FlutterLoader`](https://cs.opensource.google/flutter/engine/+/master:shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java)
+class locates and loads the libflutter.so library.
+
+## Description of change
+
+https://github.com/flutter/engine/commit/15f5696c4139a21e1fc54014ce17d01f6ad1737c#diff-599e1d64442183ead768757cca6805c3L154
+removes the `FlutterMain.setIsRunningInRobolectricTest()` testing function.
+
+https://github.com/flutter/engine/commit/15f5696c4139a21e1fc54014ce17d01f6ad1737c#diff-f928557f2d60773a8435366400fa42ed
+adds a `FlutterInjector` class to assist testing.
+
+https://github.com/flutter/engine/pull/20473 further refactors FlutterLoader and FlutterJNI
+to allow for additional mocking/testing.
+
+## Migration guide
+
+Code before migration:
+
+```java
+FlutterMain.setIsRunningInRobolectricTest(true);
+```
+
+Code after migration:
+
+```java
+FlutterJNI mockFlutterJNI = mock(FlutterJNI.class);
+FlutterInjector.setInstance(
+        new FlutterInjector.Builder()
+            .setFlutterLoader(new FlutterLoader(mockFlutterJNI))
+            .build());
+```
+
+## Timeline
+
+Landed in version: 1.22.0-2.0.pre.133<br>
+In stable release: not yet

src/docs/release/breaking-changes/index.md

@@ -17,9 +17,11 @@ release, and listed in alphabetical order:
 * [Network Policy on iOS and Android][]
 * [SnackBars managed by the ScaffoldMessenger][]
 * [TextSelectionTheme migration][]
+* [Android FlutterMain.setIsRunningInRobolectricTest testing API removed][]
 * [Clip behavior][]
 
 [Android ActivityControlSurface attachToActivity signature change]: /docs/release/breaking-changes/android-activity-control-surface-attach
+[Android FlutterMain.setIsRunningInRobolectricTest testing API removed]: /docs/release/breaking-changes/android-setIsRunningInRobolectricTest-removed
 [Material Chip button semantics]: /docs/release/breaking-changes/material-chip-button-semantics
 [Network Policy on iOS and Android]: /docs/release/breaking-changes/network-policy-ios-android
 [SnackBars managed by the ScaffoldMessenger]:  /docs/release/breaking-changes/scaffold-messenger