CONDITIONAL EXPRESSIONS, string == pattern

[scowles@ckhb.org]

I would like to execute test on patterns that are dynamically generated and that 
change between invocations depending on other data.  When I generate a scalar 
parameter containing the pattern, construct the test statement, then invoke it, 
the test fails.  However, if I force an eval on the test statement, the test 
succeeds.  I do not understand zsh parsing in this case.  Could someone please 
let me know the mechanics I am missing?

thanks very much.

zsh version:  5.8, patch 460
platform:  x64, ubu 21.04, current patches

# test code begin:

unset vs vp r
local -a r

vs=' str1  a2'
vp=
vp+=[[:blank:]]##
vp+=str1
vp+=[[:blank:]]##
vp+=[[:alnum:]]
vp+=[[:alnum:]]

r=( ${(f)"$( eval echo 'test ${vs} == ${vp} && echo hi || echo lo' )"} )
echo ${r[-1]}

test ${vs} == ${vp} && echo hi || echo lo

# test code end.

first test output:   hi
second test output:  lo