TestFormats finds potential (Printf, etc.) format strings.
If they are used in a call, the format verbs are verified
based on the matching argument type against a precomputed
table of valid formats (formatMapping, below). The table
can be used to automatically rewrite format strings with
the -u flag.
Run as: go test -run Formats [-u]
A formatMapping based on the existing formats is printed
when the test is run in verbose mode (-v flag). The table
needs to be updated whenever a new (type, format) combination
is found and the format verb is not 'v' (as in "%v").
Known bugs:
- indexed format strings ("%[2]s", etc.) are not suported
(the test will fail)
- format strings that are not simple string literals cannot
be updated automatically
(the test will fail with respective warnings)