cleanup(pubsub): explain mysterious 20 in tests

src/pubsub/src/subscriber/session.rs

@@ -827,6 +827,9 @@ mod tests {
 
     #[tokio::test(start_paused = true)]
     async fn retry_transient_when_starting_stream() -> anyhow::Result<()> {
+        // The policy should retry forever. Our default retry policies have an
+        // attempt limit of 10. So we arbitrarily pick a number greater than 10
+        // for this test.
         const NUM_RETRIES: u32 = 20;
 
         let start_time = tokio::time::Instant::now();

src/pubsub/src/subscriber/stream.rs

@@ -296,7 +296,8 @@ mod tests {
         let mut mock_stub = MockStub::new();
         let mut mock_backoff = MockBackoffPolicy::new();
         for attempt in 1..20 {
-            // Simulate N transient errors + N backoffs.
+            // Simulate N transient errors + N backoffs. We arbitrarily pick an
+            // N > 10 (the default attempt limit for GAPICs).
             mock_stub
                 .expect_streaming_pull()
                 .times(1)
@@ -338,7 +339,8 @@ mod tests {
         let mut mock_stub = MockStub::new();
         let mut mock_backoff = MockBackoffPolicy::new();
         for attempt in 1..20 {
-            // Simulate N transient errors + N backoffs.
+            // Simulate N transient errors + N backoffs. We arbitrarily pick an
+            // N > 10 (the default attempt limit for GAPICs).
             mock_stub
                 .expect_streaming_pull()
                 .times(1)