Add isolated tests for Mohawks include-default patch

t/maniskip.include-default.t

@@ -0,0 +1,41 @@
+use strict;
+use warnings;
+
+use Test::More tests => 3;
+use ExtUtils::Manifest qw( maniskip );
+
+# ABSTRACT: Ensure include-default is memory only
+
+use lib 't/tlib';
+use Test::TempDir::Tiny;
+use Cwd qw( getcwd );
+
+my $cwd = getcwd();
+END { chdir $cwd }
+
+my $tempdir = tempdir();
+chdir $tempdir;
+
+{
+  open my $fh, '>', 'MANIFEST.SKIP' or die "Can't open MANIFEST.SKIP for writing. $!";
+  print {$fh} qq[#!include_default] or die "Error writing to MANIFEST.SKIP. $!";
+  close $fh or die "Error closing MANIFEST.SKIP. $!"
+}
+
+my $skipchk = maniskip();
+
+my $skipcontents;
+{
+  open my $fh, '<', 'MANIFEST.SKIP' or die "Can't open MANIFEST.SKIP for reading. $!";
+  local $/ = undef;
+  $skipcontents = <$fh>;
+  close $fh or warn "Error closing MANIFEST.SKIP. $!";
+}
+
+unlike( $skipcontents, qr/#!start\s*included/, 'include_default not expanded on disk' );
+
+ok( $skipchk->('Makefile'),     'Makefile still skipped by default' );
+ok( !$skipchk->('Makefile.PL'), 'Makefile.PL still not skipped by default' );
+
+done_testing;
+