JAVA-2108: Check for both err and errmsg fields in WriteConcernException

   Necessary since one of these can come from either a getlasterror command, which puts the error in the err field, or a normal command like createIndexes, which puts the error in the errmsg field.

Author: jyemin

src/main/com/mongodb/WriteConcernException.java

@@ -57,7 +57,13 @@ public ServerAddress getServerAddress() {
      * @return the error message
      */
     public String getErrorMessage() {
-        return commandResult.getString("err");
+        if (commandResult.containsField("err")) {
+            return commandResult.getString("err");
+        } else if (commandResult.containsField("errmsg")) {
+            return commandResult.getString("errmsg");
+        } else {
+            return null;
+        }
     }
 
     /**

src/test/com/mongodb/DBCollectionTest.java

@@ -456,7 +456,7 @@ public void testEnsureIndexExceptions(){
         collection.ensureIndex(new BasicDBObject("x", 1), new BasicDBObject("unique", true));
     }
 
-    @Test(expected = DuplicateKeyException.class)
+    @Test
     public void testCreateIndexExceptions(){
         collection.insert(new BasicDBObject("x", 1));
         collection.insert(new BasicDBObject("x", 1));
@@ -468,7 +468,12 @@ public void testCreateIndexExceptions(){
             fail("Trying to create an existing index should not fail.");
         }
 
-        collection.createIndex(new BasicDBObject("x", 1), new BasicDBObject("unique", true));
+        try {
+            collection.createIndex(new BasicDBObject("x", 1), new BasicDBObject("unique", true));
+            fail("Should throw an exception creating unique index when there are duplicate keys");
+        } catch (DuplicateKeyException e) {
+            assertNotNull("missing error message", e.getErrorMessage());
+        }
     }
 
     @Test

src/test/com/mongodb/DuplicateKeyExceptionTest.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2016 MongoDB, Inc.
+ *
+ * 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 com.mongodb;
+
+import com.mongodb.util.TestCase;
+import org.codehaus.groovy.tools.shell.Command;
+import org.junit.Test;
+
+import java.net.UnknownHostException;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class DuplicateKeyExceptionTest extends TestCase {
+
+    @Test
+    public void shouldGetErrorMessageFromErrField() throws UnknownHostException {
+        // given
+        String err = "This is an err";
+        CommandResult result = new CommandResult(new ServerAddress());
+        result.put("err", err);
+
+        // when
+        DuplicateKeyException e = new DuplicateKeyException(result);
+
+        // then
+        assertEquals(err, e.getErrorMessage());
+    }
+
+    @Test
+    public void shouldGetErrorMessageFromErrMsgField() throws UnknownHostException {
+        // given
+        String err = "This is an err";
+        CommandResult result = new CommandResult(new ServerAddress());
+        result.put("errmsg", err);
+
+        // when
+        DuplicateKeyException e = new DuplicateKeyException(result);
+
+        // then
+        assertEquals(err, e.getErrorMessage());
+    }
+}