Improve slimming checks and integration

Change-Id: I96f0c6814e27c2caebff6a0b5ddb8c5284b66c0a
diff --git a/t/slim.t b/t/slim.t
index b79743a..f2fc78e 100644
--- a/t/slim.t
+++ b/t/slim.t
@@ -11,5 +11,13 @@
 
 ok($cache);
 
+$cache = CHI->new(driver => 'File');
+
+ok($cache);
+
+$cache = CHI->new(driver => 'FastMmap');
+
+ok($cache);
+
 done_testing;
 __END__