Allow merge of MockMultipart- w/ Mock- request builder

Issue: SPR-10280

spring-test-mvc/src/main/java/org/springframework/test/web/servlet/request/MockMultipartHttpServletRequestBuilder.java

@@ -84,15 +84,16 @@ public class MockMultipartHttpServletRequestBuilder extends MockHttpServletReque
 		if (parent == null) {
 			return this;
 		}
-		if (!(parent instanceof MockMultipartHttpServletRequestBuilder)) {
+		if (parent instanceof MockHttpServletRequestBuilder) {
+			super.merge(parent);
+			if (parent instanceof MockMultipartHttpServletRequestBuilder) {
+				MockMultipartHttpServletRequestBuilder parentBuilder = (MockMultipartHttpServletRequestBuilder) parent;
+				this.files.addAll(parentBuilder.files);
+			}
+		}
+		else {
 			throw new IllegalArgumentException("Cannot merge with [" + parent.getClass().getName() + "]");
 		}
-
-		super.merge(parent);
-
-		MockMultipartHttpServletRequestBuilder parentBuilder = (MockMultipartHttpServletRequestBuilder) parent;
-		this.files.addAll(parentBuilder.files);
-
 		return this;
 	}
 

spring-test-mvc/src/test/java/org/springframework/test/web/servlet/request/MockMultipartHttpServletRequestBuilderTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2004-2013 the original author or authors.
+ *
+ * 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.springframework.test.web.servlet.request;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import org.junit.Test;
+import org.springframework.http.HttpMethod;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockServletContext;
+
+
+/**
+ * Test fixture for {@link MockMultipartHttpServletRequestBuilder}.
+ *
+ * @author Rossen Stoyanchev
+ */
+public class MockMultipartHttpServletRequestBuilderTests {
+
+
+	@Test
+	public void test() {
+		MockHttpServletRequestBuilder parent = new MockHttpServletRequestBuilder(HttpMethod.GET, "/");
+		parent.characterEncoding("UTF-8");
+		Object result = new MockMultipartHttpServletRequestBuilder("/fileUpload").merge(parent);
+
+		assertNotNull(result);
+		assertEquals(MockMultipartHttpServletRequestBuilder.class, result.getClass());
+
+		MockMultipartHttpServletRequestBuilder builder = (MockMultipartHttpServletRequestBuilder) result;
+		MockHttpServletRequest request = builder.buildRequest(new MockServletContext());
+
+		assertEquals("UTF-8", request.getCharacterEncoding());
+	}
+
+}