No matter what kind of website you run, it’s important to test it on a regular basis.  There are several reasons for this:

1. Hosting changes – your hosting provider could tweak settings, or make bigger changes without telling you.  Any of these could break the functioning of your site in some way.
2. Programming changes – any changes you and/or your programmer makes can have unintended consequences.  Something could break in an unrelated area.
3. 3rd Party changes – any 3rd party sites that you integrate with – Facebook, authorize.net (credit card processors), ad servers, etc. can modify how their API’s work.  If this happens, your site may break.

I often have clients notice an issue with their site and I ask “when did this first occur?” and they aren’t sure.  In some cases, I can tell the site has been like that for months, maybe years.  The client simply never noticed the problem, until a customer pointed it out.

So, how should you do this?  Come up with a plan for testing various and critical parts of your site.  If you are an ecommerce provider, this means actual transactions.  Set up a coupon that let’s you buy something for a few dollars, and put through a transaction using all payment types you accept.  Test all relevant components of your site.  The frequency of the test should be related to how important the site is to your business.

Doing this routine  testing has the side effect of giving you a chance to review your customer experience, noticing areas that might be improved.  But it is important to keep a close eye on how your site functions.