R help - Jul 2012 - [rjson] toJSON serializes double as int

I have this object:
> obj <- list(test=1.0)
> obj
$test
[1] 1
> toJSON(obj)
[1] "{\"test\":1}"

How do force the serialization of obj$test to be "1.0" instead of
"1"?
I.e. the output should be:
> toJSON(obj)
[1] "{\"test\":1.0}"

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