documentclass[12pt]{article}
usepackage[onehalfspacing]{setspace}
usepackage{longtable,booktabs}

  setlengthLTpre{5em}
  setlengthLTpost{5em}

usepackage{caption}
captionsetup{font={singlespacing,small}}
captionsetup[table]{position=top,skip={0pt}}
captionsetup[longtable]{skip=0pt}


title{test}
begin{document}
This is a test table.  % repeat the paragraph to make the table at the end of a page.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

This is a test table.

begin{longtable}[]{@{}cl@{}}
caption{test table test table test tabletest tabletest tabletest tabletest tabletest tabletest tabletest tabletest tabletest tabletest table}tabularnewline
toprule
col1 & col2tabularnewline
midrule
endhead
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
1 & 2tabularnewline
bottomrule
end{longtable}


End of the document.
end{document}