[ONOS-3601] Add unit test for MetricCodec and correct some typos

Change-Id: I72317b3d2ea8c428bcc24aa215ae97c098a38305
diff --git a/web/api/src/test/java/org/onosproject/rest/MetricsResourceTest.java b/web/api/src/test/java/org/onosproject/rest/MetricsResourceTest.java
index 57c68cf..49cfa89 100644
--- a/web/api/src/test/java/org/onosproject/rest/MetricsResourceTest.java
+++ b/web/api/src/test/java/org/onosproject/rest/MetricsResourceTest.java
@@ -122,8 +122,8 @@
     }
 
     /**
-     * Hamcrest matcher to check that an device representation in JSON matches
-     * the actual device.
+     * Hamcrest matcher to check that a metric representation in JSON matches
+     * the actual metric.
      */
     public static class MetricJsonMatcher extends TypeSafeMatcher<JsonObject> {
         private final Metric metric;