json: test handling of duplicate keys

We want to see in the output when keys are used more than once. This should be
fixed because parsing the log messages as JSON will only preserve one of the
values.

staging/src/k8s.io/component-base/logs/json/json_test.go

@@ -65,6 +65,11 @@ func TestZapLoggerInfo(t *testing.T) {
 			names:  []string{"hello", "world"},
 			format: "{\"ts\":%f,\"logger\":\"hello.world\",\"caller\":\"json/json_test.go:%d\",\"msg\":\"test for WithName\",\"v\":0}\n",
 		},
+		{
+			msg:        "test for duplicate keys",
+			format:     "{\"ts\":%f,\"caller\":\"json/json_test.go:%d\",\"msg\":\"test for duplicate keys\",\"v\":0,\"akey\":\"avalue\",\"akey\":\"anothervalue\"}\n",
+			keysValues: []interface{}{"akey", "avalue", "akey", "anothervalue"},
+		},
 	}
 
 	for _, data := range testDataInfo {