How can I test that the default cache is working correctly?

[PaddyDisplays]

I changed "Enable External Cache" to "no" and flushed the cache for a few mins to see if that effected loading times, but they were about the same. Is that an effective way of testing if the cache is being using?

(I know the cache files are being created ok, I can see them in FTP, I just suspect that they are not being used when loading the pages)

[robfico]

You can flush the cache, hit one page on your site, and then verify cache files were created via FTP/ssh. This should show you the cache is working and populating on catalog page loads.

You can examine contents of files looking for keys if you really want to. Check out:

http://www.magentocommerce.com/wiki/development/block_cache_and_html_ouput

Also, you can use developer mode in your browser to look at page speed timing for cleared cache, then reloading the page 2 more times checking timing to see if it decreases due to caching. If you have a smal catalog or just simple products, load times between cached and uncached aren't that much different.

[JLHC]

Magento's built-in caching system will not make a huge difference especially for a small store. 

Have you considered using a Full Page Cache solution instead? 

[MartySMageMojo]

@JLHC Try running a store with no cache at all, it won't be very fast. The default cache is pretty good if your site is small and optimized.

But an FPC is an easy addition, like Lesti FPC.

If you need to check settings, n98 tools is very useful https://github.com/netz98/n98-magerun