public ModificationStatus doModify(FieldValue fv) {
            if (fv instanceof StringFieldValue) {
                fv.assign("newvalue");
                return ModificationStatus.MODIFIED;
            }

            return ModificationStatus.NOT_MODIFIED;
        }
Test for Document and all its features, including (de)serialization.

@author Thomas Gundersen
@author bratseth
document/src/test/java/com/yahoo/document/DocumentTestCase.java