CPP-943: Fix intermittent failures of SchemaAgreementUnitTest.Simple (#512)

The test stops cluster nodes and then performs queries. It is possible for that query to start being executed before the session detects the connection going down, resulting in test failures.

https://datastax-oss.atlassian.net/browse/CPP-943

Author: wash-amzn

tests/src/unit/tests/test_schema_agreement.cpp

@@ -55,7 +55,8 @@ class SchemaAgreementUnitTest : public LoopTest {
   static void execute(Session* session, const String& query) {
     Future::Ptr request_future(session->execute(QueryRequest::ConstPtr(new QueryRequest(query))));
     EXPECT_TRUE(request_future->wait_for(WAIT_FOR_TIME));
-    EXPECT_FALSE(request_future->error());
+    EXPECT_FALSE(request_future->error()) << cass_error_desc(request_future->error()->code) << ": "
+                                          << request_future->error()->message;
   }
 
   struct SchemaVersionCheckCounts {
@@ -191,12 +192,16 @@ TEST_F(SchemaAgreementUnitTest, Simple) {
   EXPECT_EQ(logging_criteria_count(), 1);
 
   cluster.stop(2);
+  // Give time for the session to see and react to the socket close, otherwise the next
+  // query can wind up getting a "Request timed out" error if the close happens mid-flight
+  test::Utils::msleep(100);
   execute(&session, "DROP TABLE tbl");
   EXPECT_EQ(check_counts.local_count.load(), 2);
   EXPECT_EQ(check_counts.peers_count.load(), 2);
   EXPECT_EQ(logging_criteria_count(), 2);
 
   cluster.stop(3);
+  test::Utils::msleep(100);
   execute(&session, "CREATE TABLE tbl (key text PRIMARY KEY, value text)");
   EXPECT_EQ(check_counts.local_count.load(), 3);
   EXPECT_EQ(check_counts.peers_count.load(), 3);