...or your users will!
"Doing Terrible Things To Your Code http://blog.codinghorror.com/doing-terrible-things-to-your-code/" is a good read on testing by Jeff Atwood on his blog, Coding Horror http://blog.codinghorror.com/. I also found the "falsehood" snippets poignant—maybe we should come up with some for Wikipedia ;-). Here are a couple off the top of my head, at least for "official" Wikipedia instances:
1. Wikipedia sites all have standard ISO/BFC prefixes (see sitematrix https://www.mediawiki.org/wiki/Special:SiteMatrix) 2. A site's main page is always titled "Main Page" (also see sitematrix) 3. A page's revision is a reliable snapshot of its content (nope: transclusions [and images?] can change independent of a page revision) 4. API error messages are plain text (nope, can contain HTML https://phabricator.wikimedia.org/T107082)
Interested in hearing "falsehoods" you've encountered.
Cheers,
Brian