Question about testing with variable operators

[Steven W. Orr]

I am using arithmetic tests where the test operator is passed in as an arg and 
it works just fine.

foo()
{
    (( $1 $2 $3 ))
}

foo 5 '>' 7

But I figured that if this works for arithmetic, it should also work with the 
test operator. It seems to not work:

514 > bar()
> {
>     [[ $1 $2 ]]
bash: conditional binary operator expected
bash: syntax error near `$2'

As a work around, I can use eval or the builtin test, but my question is this: 
Is this a bug or is there a reason that it should work for arithmetic but not 
for the test [[ operator?

GNU bash, version 4.0.35(1)-release (x86_64-redhat-linux-gnu)

TIA

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