🚀 Feature

Motivation

Currently fast_dev_run accept only a boolean value.

fast_dev_run meaning: Runs 1 batch of train, test and val to find any bugs (ie: a sort of unit test).

Trainer(fast_dev_run=True)

The new feature will extend fast_dev_run to accept a integer representing the number of batches to use for fast_dev_run allowing better coverage for unit testing.

Trainer(fast_dev_run=2 )

Therefore,

if isinstance(fast_dev_run, int):
    num_batches_for_fast_dev_run = fast_dev_run
    fast_dev_run = fast_dev_run > 0

Pitch

fast_dev_run is really useful for debugging and unit testing. However, sometimes, we want to make aggregation over several batches to make sure everything is correct handled.
Setting fast_dev_run =2 could allow to run 2 batch of train, test and val to find any bugs (ie: better coverage).

Alternatives

Additional context