Add isolated tests for Mohawks include-default patch

t/maniskip.include-default.t

@@ -0,0 +1,26 @@
+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 qw( in_tempdir );
+use ByteSlurper qw( write_bytes read_bytes );
+
+in_tempdir 'no-default-expansions' => sub {
+
+    write_bytes( 'MANIFEST.SKIP', qq[#!include_default] );
+
+    my $skipchk = maniskip();
+
+    my $skipcontents = read_bytes('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;