refactor(e2e): Add additional check to a flakey test

This test fails a later assertion that the device's reported property is the expected value, but this may be because the twin had more than one reported property. This check allows us to debug if the test is failing because of that reason

Author: timtay-microsoft

iot-e2e-tests/common/src/test/java/tests/integration/com/microsoft/azure/sdk/iot/iothub/MultiplexingClientTests.java

@@ -911,7 +911,8 @@ private static void testReportedPropertiesFlow(DeviceClient deviceClient, TwinCl
         Twin serviceClientTwin = twinClientServiceClient.get(deviceClient.getConfig().getDeviceId());
 
         com.microsoft.azure.sdk.iot.service.twin.TwinCollection retrievedReportedProperties = serviceClientTwin.getReportedProperties();
-        assertTrue(retrievedReportedProperties.size() > 0);
+        assertTrue("Twin had no reported properties", retrievedReportedProperties.size() > 0);
+        assertEquals("Twin had more reported properties than expected", 1, retrievedReportedProperties.size());
         String retrievedReportedPropertyKey = retrievedReportedProperties.keySet().iterator().next();
         assertEquals(expectedPropertyKey, retrievedReportedPropertyKey);
         String actualReportedPropertyValue = (String) retrievedReportedProperties.get(retrievedReportedPropertyKey);