We are going to modify the main tests table and for every case (e.g.
int(1) add pickles with various encoding that all represent the same
object when decoded. The main TestDecode driver will iterate over all
those input data and hand it over for particular testing to testDecode
worker.

Use t.Run for spawning each case - it is less typing (we do not need to
manually print test.name on errors, etc), and it allows to select which
subtests to run via e.g. `go test -run Decode/int`