Trying before you build on it.
WHY
Documentation and screenshots do not tell you whether an application suits how you work. Using it does.
Discovering a platform does not fit after three months of building is expensive.
HOW TO TEST
Install it on a subdomain, not on your live domain Put in realistic content, not sample data Perform the tasks you will actually do daily Have whoever will maintain it try it
WHAT TO TEST FOR
Can you do what you need without fighting it Is the administration comprehensible to whoever will use it Does it perform acceptably with realistic content volume Does the extension you need actually exist and work Does email send Does it export your content, in case you later move
TIMEFRAME
A week of genuine use tells you more than a month of reading.
AFTERWARDS
Remove the test installation properly: files, database, database user, subdomain.
An abandoned test installation is unpatched software sitting on your account, and this is a common way they accumulate.