Fix problems detected by the latest version of errorprone

Change-Id: I532d3627fa232e93ee6860bd10db64c99e78f915
diff --git a/utils/misc/src/test/java/org/onlab/util/CounterTest.java b/utils/misc/src/test/java/org/onlab/util/CounterTest.java
index e62672d..491b632 100644
--- a/utils/misc/src/test/java/org/onlab/util/CounterTest.java
+++ b/utils/misc/src/test/java/org/onlab/util/CounterTest.java
@@ -96,7 +96,8 @@
                 .addEqualityGroup(tt, same)
                 .addEqualityGroup(400)
                 .addEqualityGroup("")
-                .addEqualityGroup(diff);
+                .addEqualityGroup(diff)
+                .testEquals();
 
     }