Fixes a flake with the LoadReporter end2end test. (#29383)

* Fixes a flake with the LoadReporter end2end test.

I *believe* the test is wrong, based on the .proto description of the
LoadReporter.

The protocol described in src/proto/grpc/lb/v1/load_reporter.proto has
the ReportLoad rpc returns a stream of LoadReportResponse, which itself
has a repeated field of Load messages. The comment before it states:

"It is not strictly necessary to aggregate all entries into one entry
per <tag, user_id> tuple, although it is preferred to do so."

Debugging the issue shows we are in fact properly getting all 3 expected
load report types, just in two separate messages instead of a single
one.

This new test codepath will coalesce the load report responses, and also
addresses the fact the original test wasn't verifying that we were
getting the 3 expected types.

* Automated change: Fix sanity tests

* Renaming variables.

* ASSERT_ -> EXPECT_

* Automated change: Fix sanity tests

test/cpp/end2end/server_load_reporting_end2end_test.cc

@@ -142,41 +142,52 @@ TEST_F(ServerLoadReportingEnd2endTest, BasicReport) {
   const std::string& lb_id = response.initial_response().load_balancer_id();
   gpr_log(GPR_INFO, "Initial response received (lb_id: %s).", lb_id.c_str());
   ClientMakeEchoCalls(lb_id, "LB_TAG", kOkMessage, 1);
-  while (true) {
+
+  unsigned load_count = 0;
+  bool got_in_progress = false;
+  bool got_orphaned = false;
+  bool got_calls = false;
+  while (load_count < 3) {
     stream->Read(&response);
-    if (!response.load().empty()) {
-      ASSERT_EQ(response.load().size(), 3) << response.DebugString();
-      for (const auto& load : response.load()) {
-        if (load.in_progress_report_case()) {
-          // The special load record that reports the number of in-progress
-          // calls.
-          ASSERT_EQ(load.num_calls_in_progress(), 1);
-        } else if (load.orphaned_load_case()) {
-          // The call from the balancer doesn't have any valid LB token.
-          ASSERT_EQ(load.orphaned_load_case(), load.kLoadKeyUnknown);
-          ASSERT_EQ(load.num_calls_started(), 1);
-          ASSERT_EQ(load.num_calls_finished_without_error(), 0);
-          ASSERT_EQ(load.num_calls_finished_with_error(), 0);
-        } else {
-          // This corresponds to the calls from the client.
-          ASSERT_EQ(load.num_calls_started(), 1);
-          ASSERT_EQ(load.num_calls_finished_without_error(), 1);
-          ASSERT_EQ(load.num_calls_finished_with_error(), 0);
-          ASSERT_GE(load.total_bytes_received(), sizeof(kOkMessage));
-          ASSERT_GE(load.total_bytes_sent(), sizeof(kOkMessage));
-          ASSERT_EQ(load.metric_data().size(), 1);
-          ASSERT_EQ(load.metric_data().Get(0).metric_name(), kMetricName);
-          ASSERT_EQ(load.metric_data().Get(0).num_calls_finished_with_metric(),
-                    1);
-          ASSERT_EQ(load.metric_data().Get(0).total_metric_value(),
-                    kMetricValue);
-        }
+    for (const auto& load : response.load()) {
+      load_count++;
+      if (load.in_progress_report_case()) {
+        // The special load record that reports the number of in-progress
+        // calls.
+        EXPECT_EQ(load.num_calls_in_progress(), 1);
+        EXPECT_FALSE(got_in_progress);
+        got_in_progress = true;
+      } else if (load.orphaned_load_case()) {
+        // The call from the balancer doesn't have any valid LB token.
+        EXPECT_EQ(load.orphaned_load_case(), load.kLoadKeyUnknown);
+        EXPECT_EQ(load.num_calls_started(), 1);
+        EXPECT_EQ(load.num_calls_finished_without_error(), 0);
+        EXPECT_EQ(load.num_calls_finished_with_error(), 0);
+        EXPECT_FALSE(got_orphaned);
+        got_orphaned = true;
+      } else {
+        // This corresponds to the calls from the client.
+        EXPECT_EQ(load.num_calls_started(), 1);
+        EXPECT_EQ(load.num_calls_finished_without_error(), 1);
+        EXPECT_EQ(load.num_calls_finished_with_error(), 0);
+        EXPECT_GE(load.total_bytes_received(), sizeof(kOkMessage));
+        EXPECT_GE(load.total_bytes_sent(), sizeof(kOkMessage));
+        EXPECT_EQ(load.metric_data().size(), 1);
+        EXPECT_EQ(load.metric_data().Get(0).metric_name(), kMetricName);
+        EXPECT_EQ(load.metric_data().Get(0).num_calls_finished_with_metric(),
+                  1);
+        EXPECT_EQ(load.metric_data().Get(0).total_metric_value(), kMetricValue);
+        EXPECT_FALSE(got_calls);
+        got_calls = true;
       }
-      break;
     }
   }
+  EXPECT_EQ(load_count, 3);
+  EXPECT_TRUE(got_in_progress);
+  EXPECT_TRUE(got_orphaned);
+  EXPECT_TRUE(got_calls);
   stream->WritesDone();
-  ASSERT_EQ(stream->Finish().error_code(), StatusCode::CANCELLED);
+  EXPECT_EQ(stream->Finish().error_code(), StatusCode::CANCELLED);
 }
 
 // TODO(juanlishen): Add more tests.