Added one unittest to test_abox for trailing_text
Added one unittest to test_abox for trailing_text

mitocw/latex2edx,jefrench/latex2edx,evheubel/latex2edx,evheubel/latex2edx,mitocw/latex2edx,jefrench/latex2edx,mitocw/latex2edx,evheubel/latex2edx,jefrench/latex2edx