Add tests for Buf.push
Add tests for Buf.push

This addresses RT #125182

b2gills/roast,dankogai/roast,bitrauser/roast,zostay/roast,zostay/roast,dogbert17/roast,dankogai/roast,bitrauser/roast,cygx/roast,laben/roast,cygx/roast,dankogai/roast,niner/roast,b2gills/roast,b2gills/roast,laben/roast,niner/roast,perl6/roast,niner/roast,skids/roast,zostay/roast,cygx/roast,laben/roast,dogbert17/roast,skids/roast,skids/roast