Cause a failure when field's documented and actual types do not match

Closes gh-276

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/AbstractFieldsSnippet.java

@@ -100,8 +100,15 @@ public abstract class AbstractFieldsSnippet extends TemplatedSnippet {
 		validateFieldDocumentation(contentHandler);
 
 		for (FieldDescriptor descriptor : this.fieldDescriptors) {
-			if (descriptor.getType() == null) {
-				descriptor.type(contentHandler.determineFieldType(descriptor.getPath()));
+			try {
+				descriptor.type(contentHandler.determineFieldType(descriptor));
+			}
+			catch (FieldDoesNotExistException ex) {
+				String message = "Cannot determine the type of the field '"
+						+ descriptor.getPath() + "' as it is not present in the "
+						+ "payload. Please provide a type using "
+						+ "FieldDescriptor.type(Object type).";
+				throw new FieldTypeRequiredException(message);
 			}
 		}
 

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/ContentHandler.java

@@ -50,12 +50,12 @@ interface ContentHandler {
 	String getUndocumentedContent(List<FieldDescriptor> fieldDescriptors);
 
 	/**
-	 * Returns the type of the field with the given {@code path} based on the content of
-	 * the payload.
+	 * Returns the type of the field that is described by the given
+	 * {@code fieldDescriptor} based on the content of the payload.
 	 *
-	 * @param path the field path
+	 * @param fieldDescriptor the field descriptor
 	 * @return the type of the field
 	 */
-	Object determineFieldType(String path);
+	Object determineFieldType(FieldDescriptor fieldDescriptor);
 
 }

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/FieldTypesDoNotMatchException.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2014-2016 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.restdocs.payload;
+
+/**
+ * A {@code FieldTypesDoNotMatchException} is thrown when the documented and actual types
+ * of a field do not match.
+ *
+ * @author Andy Wilkinson
+ */
+class FieldTypesDoNotMatchException extends RuntimeException {
+
+	/**
+	 * Creates a new {@code FieldTypesDoNotMatchException} for the field described by the
+	 * given {@code fieldDescriptor} that has the given {@code actualType}.
+	 *
+	 * @param fieldDescriptor the field
+	 * @param actualType the actual type of the field
+	 */
+	FieldTypesDoNotMatchException(FieldDescriptor fieldDescriptor, Object actualType) {
+		super("The documented type of the field '" + fieldDescriptor.getPath() + "' is "
+				+ fieldDescriptor.getType() + " but the actual type is " + actualType);
+	}
+
+}

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/JsonContentHandler.java

@@ -34,6 +34,8 @@ class JsonContentHandler implements ContentHandler {
 
 	private final JsonFieldProcessor fieldProcessor = new JsonFieldProcessor();
 
+	private final JsonFieldTypeResolver fieldTypeResolver = new JsonFieldTypeResolver();
+
 	private final ObjectMapper objectMapper = new ObjectMapper()
 			.enable(SerializationFeature.INDENT_OUTPUT);
 
@@ -93,15 +95,26 @@ class JsonContentHandler implements ContentHandler {
 	}
 
 	@Override
-	public Object determineFieldType(String path) {
+	public Object determineFieldType(FieldDescriptor fieldDescriptor) {
+		if (fieldDescriptor.getType() == null) {
+			return this.fieldTypeResolver.resolveFieldType(fieldDescriptor.getPath(),
+					readContent());
+		}
+		if (!(fieldDescriptor.getType() instanceof JsonFieldType)) {
+			return fieldDescriptor.getType();
+		}
+		JsonFieldType descriptorFieldType = (JsonFieldType) fieldDescriptor.getType();
 		try {
-			return new JsonFieldTypeResolver().resolveFieldType(path, readContent());
+			JsonFieldType actualFieldType = this.fieldTypeResolver
+					.resolveFieldType(fieldDescriptor.getPath(), readContent());
+			if (descriptorFieldType == JsonFieldType.VARIES
+					|| descriptorFieldType == actualFieldType) {
+				return descriptorFieldType;
+			}
+			throw new FieldTypesDoNotMatchException(fieldDescriptor, actualFieldType);
 		}
 		catch (FieldDoesNotExistException ex) {
-			String message = "Cannot determine the type of the field '" + path + "' as"
-					+ " it is not present in the payload. Please provide a type using"
-					+ " FieldDescriptor.type(Object type).";
-			throw new FieldTypeRequiredException(message);
+			return fieldDescriptor.getType();
 		}
 	}
 

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/XmlContentHandler.java

@@ -153,15 +153,14 @@ class XmlContentHandler implements ContentHandler {
 	}
 
 	@Override
-	public Object determineFieldType(String path) {
-		try {
-			return new JsonFieldTypeResolver().resolveFieldType(path, readPayload());
+	public Object determineFieldType(FieldDescriptor fieldDescriptor) {
+		if (fieldDescriptor.getType() != null) {
+			return fieldDescriptor.getType();
 		}
-		catch (FieldDoesNotExistException ex) {
-			String message = "Cannot determine the type of the field '" + path + "' as"
-					+ " it is not present in the payload. Please provide a type using"
-					+ " FieldDescriptor.type(Object type).";
-			throw new FieldTypeRequiredException(message);
+		else {
+			throw new FieldTypeRequiredException("The type of a field in an XML payload "
+					+ "cannot be determined automatically. Please provide a type using "
+					+ "FieldDescriptor.type(Object type)");
 		}
 	}