how to remove last comma from line in bash using "sed or awk" -

hi want remove last comma line. example:

input:

this,is,a,test 

desired output:

this,is,a test 

i able remove last comma if last character of string using below command: (however not want)

echo "this,is,a,test," |sed 's/,$//' this,is,a,test 

same command not work if there more characters past last comma in line.

echo "this,is,a,test" |sed 's/,$//' this,is,a,test 

i able achieve results using dirty way calling multiple commands, alternative achieve same using awk or sed regex ?(this want)

echo "this,is,a,test" |rev |sed 's/,/ /' |rev this,is,a test 

$ echo "this,is,a,test" | sed 's/\(.*\),/\1 /' this,is,a test 

with lookbehind,

$ echo "this,is,a,test" | perl -pe 's/.*\k,/ /' this,is,a test 

* greedy, tries match as possible.