make SubscriptionsSurviveConnectionFailureAsync more reliable; Ping is not routed to the channel, and can use primary or replica, so Ping is not a reliable test *unless* we demand master

Author: mgravell

tests/StackExchange.Redis.Tests/FailoverTests.cs

@@ -236,10 +236,12 @@ public async Task SubscriptionsSurviveConnectionFailureAsync()
         server.SimulateConnectionFailure(SimulatedFailureType.All);
         // Trigger failure (RedisTimeoutException or RedisConnectionException because
         // of backlog behavior)
-        var ex = Assert.ThrowsAny<Exception>(() => sub.Ping());
-        Assert.True(ex is RedisTimeoutException or RedisConnectionException);
         Assert.False(sub.IsConnected(channel));
 
+        var ex = Assert.ThrowsAny<Exception>(() => Log($"Ping: {sub.Ping(CommandFlags.DemandMaster)}ms"));
+        Assert.True(ex is RedisTimeoutException or RedisConnectionException);
+        Log($"Failed as expected: {ex.Message}");
+
         // Now reconnect...
         conn.AllowConnect = true;
         Log("Waiting on reconnect");