[ONOS-4798] Error Message implementation for YANG utils

Change-Id: Idb13e851258754773f8f447ace69a9393c7c1b3d
diff --git a/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ErrorMessageListnerTest.java b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ErrorMessageListnerTest.java
new file mode 100644
index 0000000..bf53292
--- /dev/null
+++ b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ErrorMessageListnerTest.java
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.junit.Test;
+import org.onosproject.yangutils.datamodel.YangMust;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangAppErrorInfo;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.YangUtilsParserManager;
+
+import java.io.IOException;
+import java.util.List;
+
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Test-cases for testing error message listener functionality.
+ */
+public class ErrorMessageListnerTest {
+    private final YangUtilsParserManager manager = new YangUtilsParserManager();
+
+    /**
+     * Checks if error message listener updates the data model.
+     */
+    @Test
+    public void processContainerSubStatementErrorMessage() throws IOException, ParserException {
+        YangNode node = manager.getDataModel("src/test/resources/ContainerSubStatementErrorMessage.yang");
+
+        YangModule yangNode = (YangModule) node;
+        assertThat(yangNode.getName(), is("ErrorMessage"));
+
+        YangContainer yangContainer = (YangContainer) yangNode.getChild();
+        assertThat(yangContainer.getName(), is("interface"));
+
+        String expectedConstraint = "ifType != 'ethernet' or (ifType = 'ethernet' and ifMTU = 1500)";
+        List<YangMust> mustConstraintList = yangContainer.getListOfMust();
+        assertThat(mustConstraintList.iterator().next().getConstraint(), is(expectedConstraint));
+
+        YangAppErrorInfo yangAppErrorInfo = mustConstraintList.iterator().next().getAppErrorInfo();
+        assertThat(yangAppErrorInfo.getGetErrorMessage(), is("An ethernet MTU must be 1500"));
+        assertThat(yangAppErrorInfo.getGetErrorTag(), is("operation-failed"));
+    }
+}