assertThat(fieldMapper, instanceOf(StringFieldMapper.class));
// Check json serialization
StringFieldMapper stringFieldMapper = (StringFieldMapper) fieldMapper;
XContentBuilder builder = jsonBuilder().startObject();
stringFieldMapper.toXContent(builder, ToXContent.EMPTY_PARAMS).endObject();
builder.close();
Map<String, Object> serializedMap = JsonXContent.jsonXContent.createParser(builder.bytes()).mapAndClose();
Map<String, Object> copyTestMap = (Map<String, Object>) serializedMap.get("copy_test");
assertThat(copyTestMap.get("type").toString(), is("string"));
List<String> copyToList = (List<String>) copyTestMap.get("copy_to");