docs: add note about directExecutor in example tests.

examples/src/test/java/io/grpc/examples/helloworld/HelloWorldClientTest.java

@@ -39,6 +39,10 @@
  * For demonstrating how to write gRPC unit test only.
  * Not intended to provide a high code coverage or to test every major usecase.
  *
+ * directExecutor() makes it easier to have deterministic tests.
+ * However, if your implementation uses another thread and uses streaming it is better to use
+ * the default executor, to avoid hitting bug #3084.
+ *
  * <p>For more unit test examples see {@link io.grpc.examples.routeguide.RouteGuideClientTest} and
  * {@link io.grpc.examples.routeguide.RouteGuideServerTest}.
  */

examples/src/test/java/io/grpc/examples/helloworld/HelloWorldServerTest.java

@@ -32,6 +32,10 @@
  * For demonstrating how to write gRPC unit test only.
  * Not intended to provide a high code coverage or to test every major usecase.
  *
+ * directExecutor() makes it easier to have deterministic tests.
+ * However, if your implementation uses another thread and uses streaming it is better to use
+ * the default executor, to avoid hitting bug #3084.
+ *
  * <p>For more unit test examples see {@link io.grpc.examples.routeguide.RouteGuideClientTest} and
  * {@link io.grpc.examples.routeguide.RouteGuideServerTest}.
  */

examples/src/test/java/io/grpc/examples/routeguide/RouteGuideClientTest.java

@@ -53,6 +53,10 @@
  * For demonstrating how to write gRPC unit test only.
  * Not intended to provide a high code coverage or to test every major usecase.
  *
+ * directExecutor() makes it easier to have deterministic tests.
+ * However, if your implementation uses another thread and uses streaming it is better to use
+ * the default executor, to avoid hitting bug #3084.
+ *
  * <p>For basic unit test examples see {@link io.grpc.examples.helloworld.HelloWorldClientTest} and
  * {@link io.grpc.examples.helloworld.HelloWorldServerTest}.
  */

examples/src/test/java/io/grpc/examples/routeguide/RouteGuideServerTest.java

@@ -49,6 +49,10 @@
  * For demonstrating how to write gRPC unit test only.
  * Not intended to provide a high code coverage or to test every major usecase.
  *
+ * directExecutor() makes it easier to have deterministic tests.
+ * However, if your implementation uses another thread and uses streaming it is better to use
+ * the default executor, to avoid hitting bug #3084.
+ *
  * <p>For basic unit test examples see {@link io.grpc.examples.helloworld.HelloWorldClientTest} and
  * {@link io.grpc.examples.helloworld.HelloWorldServerTest}.
  */