Tips for debugging: R CMD check examples

Does anyone have any suggestions for debugging the execution of
examples by R CMD check?  The examples work fine when I run them from
a live R prompt, but I get errors when they are run by R CMD check.

Not a real tip, but when it occurs I immediately
check for namespace issues (which often turn out
to be the origin). Things I do are

- verify all packages involved have namespaces;
- load all packages (i.e. put explicitly on the
   search path) to detect masking issues;
- check all imports and exports and if relevant
   turn package imports into individual function
   imports to have a more fine-grained view.

Agreed this is a very indirect way, but at times
faster than trying to interpret the error message.

Best,
Tobias