Ravenwood support for feature flags.

Since feature flags are becoming an important part of development
work, ensure that Ravenwood tests can use existing tools such as
`SetFlagsRule` to populate values for code-under-test to consume.

To enable this, we extend `AndroidHeuristicsFilter` to recognize
feature flags generated code, and include that in the Ravenwood
environment by default.

Bug: 311370221
Test: atest FrameworksCoreTestsRavenwood FrameworksCoreTests
Change-Id: I526af65f816d153cb6e365cf6810a5a304d3e6a6

2 files changed, 26 insertions, 2 deletions

diff --git a/ravenwood/framework-minus-apex-ravenwood-policies.txt b/ravenwood/framework-minus-apex-ravenwood-policies.txt
index c9069e5db9cb..f5e4af50fc29 100644
--- a/ravenwood/framework-minus-apex-ravenwood-policies.txt
+++ b/ravenwood/framework-minus-apex-ravenwood-policies.txt
@@ -3,6 +3,9 @@
 # Keep all AIDL interfaces
 class :aidl stubclass
 
+# Keep all feature flag implementations
+class :feature_flags stubclass
+
 # Collections
 class android.util.ArrayMap stubclass
 class android.util.ArraySet stubclass
diff --git a/ravenwood/test-authors.md b/ravenwood/test-authors.md
index 5adef534a2b2..de05777f01cd 100644
--- a/ravenwood/test-authors.md
+++ b/ravenwood/test-authors.md
@@ -71,10 +71,10 @@ public class MyCodeTest {
 Once you’ve defined your test, you can use typical commands to execute it locally:
 
 ```
-$ atest MyTestsRavenwood
+$ atest --host MyTestsRavenwood
 ```
 
-> **Note:** There's a known bug where `atest` currently requires a connected device to run Ravenwood tests, but that device isn't used for testing.
+> **Note:** There's a known bug where `atest` currently requires a connected device to run Ravenwood tests, but that device isn't used for testing. Using the `--host` argument above is a way to bypass this requirement until bug #312525698 is fixed.
 
 You can also run your new tests automatically via `TEST_MAPPING` rules like this:
 
@@ -89,6 +89,27 @@ You can also run your new tests automatically via `TEST_MAPPING` rules like this
 }
 ```
 
+## Strategies for feature flags
+
+Ravenwood supports writing tests against logic that uses feature flags through the existing `SetFlagsRule` infrastructure maintained by the feature flagging team:
+
+```
+import android.platform.test.flag.junit.SetFlagsRule;
+
+@RunWith(AndroidJUnit4.class)
+public class MyCodeTest {
+    @Rule
+    public final SetFlagsRule mSetFlagsRule = new SetFlagsRule();
+
+    @Test
+    public void testEnabled() {
+        mSetFlagsRule.enableFlags(Flags.FLAG_MY_FLAG);
+        // verify test logic that depends on flag being enabled
+    }
+```
+
+This naturally composes together well with any `RavenwoodRule` that your test may need.
+
 ## Strategies for migration/bivalent tests
 
 Ravenwood aims to support tests that are written in a “bivalent” way, where the same test code can run on both a real Android device and under a Ravenwood environment.