Where is your mocked module in your distribution? I typically put them in inc/mock/ and then have the toolchain tell PAUSE not to index inc/. Last I heard the Makefile.PL way to do this is to add the following to the data you pass to WriteMakeFile():

META_ADD => {
    no_index => [ qw{ inc } ],
},
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My notes say this requires Module::Build version 6.4501 or higher.

The mechanism for Build.PL is similar.