add unittests for _extend_padding
add unittests for _extend_padding

funginstitute/patentprocessor,yngcan/patentprocessor,yngcan/patentprocessor,yngcan/patentprocessor,nikken1/patentprocessor,nikken1/patentprocessor,funginstitute/patentprocessor,nikken1/patentprocessor,funginstitute/patentprocessor