You could try globbing @ARGV in a begin block:

perl -e"BEGIN{ @ARGV=map glob, @ARGV }" -le"print for @ARGV" t\*.t
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If the shell has already expanded the file arguments then the glob will have no effect, but on win32 it will expand it.

perl's glob will also expand wild cards in the paths so things like:

perl -le"BEGIN{ @ARGV= map glob, @ARGV}" -e"print for @ARGV" t/*/*.t
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Become possible should you want to structure your test directory beyond one level.