Test for null cache to improve slim images

Change-Id: Ic3699a11a498520f61c42d79da48215b60d3a376
diff --git a/t/slim.t b/t/slim.t
new file mode 100644
index 0000000..b79743a
--- /dev/null
+++ b/t/slim.t
@@ -0,0 +1,15 @@
+use Test::More;
+use strict;
+use warnings;
+
+# This is a collection of tests to trigger requirements
+# that may otherwise be removed by slimming docker images.
+
+use_ok('CHI');
+
+my $cache = CHI->new(driver => 'Null');
+
+ok($cache);
+
+done_testing;
+__END__