trainer.py

# Copyright The PyTorch Lightning team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import os
import warnings
from typing import Dict, Iterable, List, Optional, Union

import torch
from torch.utils.data import DataLoader

from pytorch_lightning.callbacks import Callback, EarlyStopping, ModelCheckpoint
from pytorch_lightning.core.datamodule import LightningDataModule
from pytorch_lightning.core.lightning import LightningModule
from pytorch_lightning.core.memory import ModelSummary
from pytorch_lightning.core.step_result import EvalResult
from pytorch_lightning.loggers import LightningLoggerBase
from pytorch_lightning.profiler import BaseProfiler
from pytorch_lightning.trainer.callback_hook import TrainerCallbackHookMixin
from pytorch_lightning.trainer.configuration_validator import ConfigValidator
from pytorch_lightning.trainer.data_loading import TrainerDataLoadingMixin
from pytorch_lightning.trainer.logging import TrainerLoggingMixin
from pytorch_lightning.trainer.model_hooks import TrainerModelHooksMixin
from pytorch_lightning.trainer.optimizers import TrainerOptimizersMixin
from pytorch_lightning.trainer.states import TrainerState, trainer_state
from pytorch_lightning.trainer.training_tricks import TrainerTrainingTricksMixin
from pytorch_lightning.utilities import rank_zero_warn
from pytorch_lightning.utilities.debugging import InternalDebugger
from pytorch_lightning.utilities.exceptions import MisconfigurationException
from pytorch_lightning.trainer.evaluation_loop import EvaluationLoop
from pytorch_lightning.trainer.training_loop import TrainLoop
from pytorch_lightning.accelerators.accelerator_connector import AcceleratorConnector
from pytorch_lightning.trainer.connectors.logger_connector import LoggerConnector
from pytorch_lightning.trainer.connectors.optimizer_connector import OptimizerConnector
from pytorch_lightning.trainer.connectors.training_trick_connector import TrainingTricksConnector
from pytorch_lightning.trainer.connectors.callback_connector import CallbackConnector
from pytorch_lightning.trainer.connectors.model_connector import ModelConnector
from pytorch_lightning.trainer.connectors.debugging_connector import DebuggingConnector
from pytorch_lightning.trainer.connectors.checkpoint_connector import CheckpointConnector
from pytorch_lightning.trainer.connectors.slurm_connector import SLURMConnector
from pytorch_lightning import _logger as log
from pytorch_lightning.tuner.tuning import Tuner
from pytorch_lightning.trainer.connectors.precision_connector import PrecisionConnector
from pytorch_lightning.trainer.connectors.profiler_connector import ProfilerConnector
from pytorch_lightning.trainer.connectors.data_connector import DataConnector
from pytorch_lightning.utilities.cloud_io import load as pl_load
from pytorch_lightning.utilities.model_utils import is_overridden
from pytorch_lightning.trainer.properties import TrainerProperties
from pytorch_lightning.cluster_environments.cluster_environment import ClusterEnvironment

# warnings to ignore in trainer
warnings.filterwarnings(
    'ignore', message='torch.distributed.reduce_op is deprecated, ' 'please use torch.distributed.ReduceOp instead'
)
os.environ['PYTHONWARNINGS'] = 'ignore:semaphore_tracker:UserWarning'

try:
    from apex import amp
except ImportError:
    amp = None


class Trainer(
    TrainerProperties,
    TrainerCallbackHookMixin,
    TrainerModelHooksMixin,
    TrainerOptimizersMixin,
    TrainerLoggingMixin,
    TrainerTrainingTricksMixin,
    TrainerDataLoadingMixin,
):
    def __init__(
        self,
        logger: Union[LightningLoggerBase, Iterable[LightningLoggerBase], bool] = True,
        checkpoint_callback: Union[ModelCheckpoint, bool] = True,
        early_stop_callback: Optional[Union[EarlyStopping, bool]] = False,  # todo: remove in v1.0.0
        callbacks: Optional[List[Callback]] = None,
        default_root_dir: Optional[str] = None,
        gradient_clip_val: float = 0,
        process_position: int = 0,
        num_nodes: int = 1,
        num_processes: int = 1,
        gpus: Optional[Union[List[int], str, int]] = None,
        auto_select_gpus: bool = False,
        tpu_cores: Optional[Union[List[int], str, int]] = None,
        log_gpu_memory: Optional[str] = None,
        progress_bar_refresh_rate: int = 1,
        overfit_batches: Union[int, float] = 0.0,
        track_grad_norm: Union[int, float, str] = -1,
        check_val_every_n_epoch: int = 1,
        fast_dev_run: bool = False,
        accumulate_grad_batches: Union[int, Dict[int, int], List[list]] = 1,
        max_epochs: int = 1000,
        min_epochs: int = 1,
        max_steps: Optional[int] = None,
        min_steps: Optional[int] = None,
        limit_train_batches: Union[int, float] = 1.0,
        limit_val_batches: Union[int, float] = 1.0,
        limit_test_batches: Union[int, float] = 1.0,
        val_check_interval: Union[int, float] = 1.0,
        log_save_interval: int = 100,
        row_log_interval: int = 50,
        distributed_backend: Optional[str] = None,
        sync_batchnorm: bool = False,
        precision: int = 32,
        weights_summary: Optional[str] = ModelSummary.MODE_DEFAULT,
        weights_save_path: Optional[str] = None,
        num_sanity_val_steps: int = 2,
        truncated_bptt_steps: Optional[int] = None,
        resume_from_checkpoint: Optional[str] = None,
        profiler: Optional[Union[BaseProfiler, bool]] = None,
        benchmark: bool = False,
        deterministic: bool = False,
        reload_dataloaders_every_epoch: bool = False,
        auto_lr_find: Union[bool, str] = False,
        replace_sampler_ddp: bool = True,
        terminate_on_nan: bool = False,
        auto_scale_batch_size: Union[str, bool] = False,
        prepare_data_per_node: bool = True,
        cluster_environment: ClusterEnvironment = None,
        amp_backend: str = 'native',
        amp_level: str = 'O2',  # backward compatible, todo: remove in v1.0.0
        overfit_pct: float = None,  # backward compatible, todo: remove in v1.0.0
    ):
        r"""
        Customize every aspect of training via flags

        Args:

            accumulate_grad_batches: Accumulates grads every k batches or as set up in the dict.

            amp_backend: The mixed precision backend to use ("native" or "apex")

            amp_level: The optimization level to use (O1, O2, etc...).

            auto_lr_find: If set to True, will make trainer.tune() run a learning rate finder,
                trying to optimize initial learning for faster convergence. trainer.tune() method will
                set the suggested learning rate in self.lr or self.learning_rate in the LightningModule.
                To use a different key set a string instead of True with the key name.

            auto_scale_batch_size: If set to True, will `initially` run a batch size
                finder trying to find the largest batch size that fits into memory.
                The result will be stored in self.batch_size in the LightningModule.
                Additionally, can be set to either `power` that estimates the batch size through
                a power search or `binsearch` that estimates the batch size through a binary search.

            auto_select_gpus: If enabled and `gpus` is an integer, pick available
                gpus automatically. This is especially useful when
                GPUs are configured to be in "exclusive mode", such
                that only one process at a time can access them.

            benchmark: If true enables cudnn.benchmark.

            callbacks: Add a list of callbacks.

            checkpoint_callback: Callback for checkpointing.

            check_val_every_n_epoch: Check val every n train epochs.

            cluster_environment: Environment config to link up arbitrary clusters

            default_root_dir: Default path for logs and weights when no logger/ckpt_callback passed.
                Default: ``os.getcwd()``.
                Can be remote file paths such as `s3://mybucket/path` or 'hdfs://path/'

            deterministic: If true enables cudnn.deterministic.

            distributed_backend: The distributed backend to use (dp, ddp, ddp2, ddp_spawn, ddp_cpu)

            early_stop_callback (:class:`pytorch_lightning.callbacks.EarlyStopping`).
                Deprecated since v0.10.0 and will be removed in v1.0.

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

            gpus: number of gpus to train on (int) or which GPUs to train on (list or str) applied per node

            gradient_clip_val: 0 means don't clip.

            limit_train_batches: How much of training dataset to check (floats = percent, int = num_batches)

            limit_val_batches: How much of validation dataset to check (floats = percent, int = num_batches)

            limit_test_batches: How much of test dataset to check (floats = percent, int = num_batches)

            logger: Logger (or iterable collection of loggers) for experiment tracking.

            log_gpu_memory: None, 'min_max', 'all'. Might slow performance

            log_save_interval: Writes logs to disk this often

            prepare_data_per_node: If True, each LOCAL_RANK=0 will call prepare data.
                Otherwise only NODE_RANK=0, LOCAL_RANK=0 will prepare data

            process_position: orders the progress bar when running multiple models on same machine.

            progress_bar_refresh_rate: How often to refresh progress bar (in steps). Value ``0`` disables progress bar.
                Ignored when a custom callback is passed to :paramref:`~Trainer.callbacks`.

            profiler:  To profile individual steps during training and assist in identifying bottlenecks.

            overfit_batches: Overfit a percent of training data (float) or a set number of batches (int). Default: 0.0

            precision: Full precision (32), half precision (16). Can be used on CPU, GPU or TPUs.

            max_epochs: Stop training once this number of epochs is reached.

            min_epochs: Force training for at least these many epochs

            max_steps: Stop training after this number of steps. Disabled by default (None).

            min_steps: Force training for at least these number of steps. Disabled by default (None).

            num_nodes: number of GPU nodes for distributed training.

            num_sanity_val_steps: Sanity check runs n validation batches before starting the training routine.
                Set it to `-1` to run all batches in all validation dataloaders. Default: 2

            reload_dataloaders_every_epoch: Set to True to reload dataloaders every epoch.

            replace_sampler_ddp: Explicitly enables or disables sampler replacement. If not specified this
                will toggled automatically when DDP is used. By default it will add ``shuffle=True`` for
                train sampler and ``shuffle=False`` for val/test sampler. If you want to customize it,
                you can set ``replace_sampler_ddp=False`` and add your own distributed sampler.

            resume_from_checkpoint: To resume training from a specific checkpoint pass in the path here.
                This can be a URL.

            row_log_interval: How often to add logging rows (does not write to disk)

            sync_batchnorm: Synchronize batch norm layers between process groups/whole world.

            terminate_on_nan: If set to True, will terminate training (by raising a `ValueError`) at the
                end of each training batch, if any of the parameters or the loss are NaN or +/-inf.

            tpu_cores: How many TPU cores to train on (1 or 8) / Single TPU to train on [1]

            track_grad_norm: -1 no tracking. Otherwise tracks that p-norm. May be set to 'inf' infinity-norm.

            truncated_bptt_steps: Truncated back prop breaks performs backprop every k steps of much longer
                sequence.

            val_check_interval: How often to check the validation set. Use float to check within a training epoch,
                use int to check every n steps (batches).

            weights_summary: Prints a summary of the weights when training begins.

            weights_save_path: Where to save weights if specified. Will override default_root_dir
                    for checkpoints only. Use this if for whatever reason you need the checkpoints
                    stored in a different place than the logs written in `default_root_dir`.
                    Can be remote file paths such as `s3://mybucket/path` or 'hdfs://path/'
                    Defaults to `default_root_dir`.
        """
        super().__init__()

        # init connectors
        self.dev_debugger = InternalDebugger(self)
        self.config_validator = ConfigValidator(self)
        self.data_connector = DataConnector(self)
        self.optimizer_connector = OptimizerConnector(self)
        self.accelerator_connector = AcceleratorConnector(self)
        self.logger_connector = LoggerConnector(self)
        self.model_connector = ModelConnector(self)
        self.precision_connector = PrecisionConnector(self)
        self.callback_connector = CallbackConnector(self)
        self.debugging_connector = DebuggingConnector(self)
        self.training_tricks_connector = TrainingTricksConnector(self)
        self.profile_connector = ProfilerConnector(self)
        self.checkpoint_connector = CheckpointConnector(self)
        self.slurm_connector = SLURMConnector(self)
        self.tuner = Tuner(self)
        self.accelerator_backend = None
        self.evaluation_loop = EvaluationLoop(self)
        self.train_loop = TrainLoop(self)

        # training state
        self.weights_summary = weights_summary
        self.model = None
        self.shown_warnings = set()

        # init callbacks
        # Declare attributes to be set in callback_connector on_trainer_init
        self.checkpoint_callback: Union[ModelCheckpoint, bool] = checkpoint_callback
        self.early_stop_callback: Optional[Union[EarlyStopping, bool]] = early_stop_callback
        self.callback_connector.on_trainer_init(
            callbacks,
            early_stop_callback,
            checkpoint_callback,
            progress_bar_refresh_rate,
            process_position,
            default_root_dir,
            weights_save_path,
            resume_from_checkpoint
        )

        # hook
        self.on_init_start()

        # init optimizer + lr scheduler related flags
        self.optimizer_connector.on_trainer_init()

        # init data flags
        self.data_connector.on_trainer_init(
            check_val_every_n_epoch,
            reload_dataloaders_every_epoch,
            prepare_data_per_node
        )

        # init training tricks
        self.training_tricks_connector.on_trainer_init(
            gradient_clip_val,
            track_grad_norm,
            accumulate_grad_batches,
            truncated_bptt_steps,
            terminate_on_nan
        )

        # init accelerator related flags
        self.accelerator_connector.on_trainer_init(
            num_processes,
            tpu_cores,
            distributed_backend,
            auto_select_gpus,
            gpus,
            num_nodes,
            log_gpu_memory,
            sync_batchnorm,
            benchmark,
            replace_sampler_ddp,
            deterministic,
            cluster_environment
        )

        # init train loop related flags
        self.train_loop.on_trainer_init(max_epochs, min_epochs, max_steps, min_steps, num_sanity_val_steps)
        self.evaluation_loop.on_trainer_init()

        # configure tuner
        self.tuner.on_trainer_init(auto_lr_find, auto_scale_batch_size)

        # configure profiler
        self.profile_connector.on_trainer_init(profiler)

        # init logger flags
        self.logger_connector.on_trainer_init(logger, log_save_interval, row_log_interval)

        # init debugging flags
        self.debugging_connector.on_init_start(
            overfit_pct,
            limit_train_batches,
            limit_val_batches,
            limit_test_batches,
            val_check_interval,
            overfit_batches,
            fast_dev_run
        )

        # set precision
        self.precision_connector.on_trainer_init(precision, amp_level, amp_backend)

        # Callback system
        self.on_init_end()

    def tune(
        self,
        model: LightningModule,
        train_dataloader: Optional[DataLoader] = None,
        val_dataloaders: Optional[Union[DataLoader, List[DataLoader]]] = None,
        datamodule: Optional[LightningDataModule] = None,
    ):
        r"""
        Runs routines to tune hyperparameters before training.

        Args:
            datamodule: A instance of :class:`LightningDataModule`.

            model: Model to tune.

            train_dataloader: A Pytorch DataLoader with training samples. If the model has
                a predefined train_dataloader method this will be skipped.

            val_dataloaders: Either a single Pytorch Dataloader or a list of them, specifying validation samples.
                If the model has a predefined val_dataloaders method this will be skipped

        """
        # setup data, etc...
        self.train_loop.setup_fit(model, train_dataloader, val_dataloaders, datamodule)

        # hook
        self.data_connector.prepare_data(model)

        # Run auto batch size scaling
        if self.auto_scale_batch_size:
            if isinstance(self.auto_scale_batch_size, bool):
                self.auto_scale_batch_size = 'power'
            self.tuner.scale_batch_size(
                model,
                mode=self.auto_scale_batch_size,
                train_dataloader=train_dataloader,
                val_dataloaders=val_dataloaders,
                datamodule=datamodule,
            )
            model.logger = self.logger  # reset logger binding

        # Run learning rate finder:
        if self.auto_lr_find:
            self.tuner.internal_find_lr(self, model)
            model.logger = self.logger  # reset logger binding

    # -----------------------------
    # MODEL TRAINING
    # -----------------------------
    def fit(
        self,
        model: LightningModule,
        train_dataloader: Optional[DataLoader] = None,
        val_dataloaders: Optional[Union[DataLoader, List[DataLoader]]] = None,
        datamodule: Optional[LightningDataModule] = None,
    ):
        r"""
        Runs the full optimization routine.

        Args:
            datamodule: A instance of :class:`LightningDataModule`.

            model: Model to fit.

            train_dataloader: A Pytorch DataLoader with training samples. If the model has
                a predefined train_dataloader method this will be skipped.

            val_dataloaders: Either a single Pytorch Dataloader or a list of them, specifying validation samples.
                If the model has a predefined val_dataloaders method this will be skipped

        """
        self._state = TrainerState.RUNNING

        # setup data, etc...
        self.train_loop.setup_fit(model, train_dataloader, val_dataloaders, datamodule)

        # hook
        self.data_connector.prepare_data(model)

        # set testing if set in environ
        self.testing = os.environ.get('PL_TESTING_MODE', self.testing)

        # -------------------------
        # TRAIN
        # -------------------------
        self.accelerator_backend = self.accelerator_connector.select_accelerator()
        self.accelerator_backend.setup(model)

        # hook
        self.call_hook('on_fit_start')

        results = self.accelerator_backend.train()
        self.accelerator_backend.teardown()

        # -------------------------
        # POST-Training
        # -------------------------
        # hook
        self.call_hook('on_fit_end')

        # hook
        self.teardown('fit')
        if self.is_function_implemented('teardown'):
            model.teardown('fit')

        # return 1 when finished
        # used for testing or when we need to know that training succeeded

        if self._state != TrainerState.INTERRUPTED:
            self._state = TrainerState.FINISHED
        return results or 1

    def train(self):
        self.run_sanity_check(self.get_model())

        # enable train mode
        model = self.get_model()
        model.train()
        torch.set_grad_enabled(True)

        # reload data when needed
        self.train_loop.reset_train_val_dataloaders(model)

        # hook
        self.train_loop.on_train_start()

        try:
            # run all epochs
            for epoch in range(self.current_epoch, self.max_epochs):

                # reset train dataloader
                if self.reload_dataloaders_every_epoch:
                    self.reset_train_dataloader(model)

                # hook
                self.train_loop.on_train_epoch_start(epoch)

                # run train epoch
                self.train_loop.run_training_epoch()

                if self.max_steps and self.max_steps <= self.global_step:

                    # hook
                    self.train_loop.on_train_end()
                    return

                # update LR schedulers
                self.optimizer_connector.update_learning_rates(interval='epoch')

                # early stopping
                met_min_epochs = epoch >= self.min_epochs - 1
                met_min_steps = self.global_step >= self.min_steps if self.min_steps else True

                if self.should_stop:
                    if (met_min_epochs and met_min_steps):
                        self.train_loop.on_train_end()
                        return
                    else:
                        log.info('Trainer was signaled to stop but required minimum epochs'
                                 f' ({self.min_epochs}) or minimum steps ({self.min_steps}) has'
                                 ' not been met. Training will continue...')

            # hook
            self.train_loop.on_train_end()

        except KeyboardInterrupt:
            rank_zero_warn('Detected KeyboardInterrupt, attempting graceful shutdown...')

            # user could press ctrl+c many times... only shutdown once
            if not self.interrupted:
                self.interrupted = True
                self._state = TrainerState.INTERRUPTED
                self.on_keyboard_interrupt()

                # hook
                self.train_loop.on_train_end()

    def run_evaluation(self, test_mode: bool = False, max_batches=None):
        # bookkeeping
        self.evaluation_loop.testing = test_mode
        dataloaders, max_batches = self.evaluation_loop.get_evaluation_dataloaders(max_batches)
        if self.evaluation_loop.should_skip_evaluation(dataloaders, max_batches):
            return [], []

        # enable eval mode + no grads
        model = self.get_model()
        self.evaluation_loop.on_evaluation_model_eval()

        model.zero_grad()
        torch.set_grad_enabled(False)

        # hook
        self.evaluation_loop.on_evaluation_start()

        # set up the eval loop
        self.evaluation_loop.setup(model, max_batches, dataloaders)

        # hook
        # TODO: should this be insider the dataloader loop?
        self.evaluation_loop.on_evaluation_epoch_start()

        # run validation/testing
        for dataloader_idx, dataloader in enumerate(dataloaders):
            # bookkeeping
            dl_outputs = []
            dl_step_metrics = []
            dataloader = self.accelerator_backend.process_dataloader(dataloader)
            dl_max_batches = self.evaluation_loop.max_batches[dataloader_idx]

            for batch_idx, batch in enumerate(dataloader):
                if batch is None:
                    continue

                # stop short when running on limited batches
                if batch_idx >= dl_max_batches:
                    break

                # hook
                self.evaluation_loop.on_evaluation_batch_start(batch, batch_idx, dataloader_idx)

                # lightning module methods
                output = self.evaluation_loop.evaluation_step(test_mode, batch, batch_idx, dataloader_idx)
                output = self.evaluation_loop.evaluation_step_end(output)

                # hook
                self.evaluation_loop.on_evaluation_batch_end(batch, batch_idx, dataloader_idx)

                # clean up
                self.evaluation_loop.evaluation_batch_end_cleanup(output, batch_idx, dataloader_idx)

                # TODO: deprecate 1.0
                self.evaluation_loop.log_evaluation_step_metrics_legacy(output, batch_idx)

                # log step metrics
                step_metrics = self.evaluation_loop.log_evaluation_step_metrics(batch, batch_idx)

                if step_metrics is not None:
                    dl_step_metrics.append(step_metrics)

                # track epoch level outputs
                if output is not None:
                    dl_outputs.append(output)

            self.evaluation_loop.outputs.append(dl_outputs)
            self.evaluation_loop.step_metrics.append(dl_step_metrics)

        # lightning module method
        deprecated_eval_results, epoch_logs = self.evaluation_loop.evaluation_epoch_end(
            num_dataloaders=len(dataloaders)
        )

        # bookkeeping
        eval_loop_results = self.evaluation_loop.log_epoch_metrics(deprecated_eval_results, epoch_logs, test_mode)
        self.evaluation_loop.predictions.to_disk()

        # hook
        self.evaluation_loop.on_evaluation_epoch_end()

        # enable train mode again
        self.evaluation_loop.on_evaluation_model_train()
        torch.set_grad_enabled(True)

        # hook
        self.evaluation_loop.on_evaluation_end()

        return eval_loop_results, deprecated_eval_results

    def run_test(self):
        # only load test dataloader for testing
        # self.reset_test_dataloader(ref_model)
        eval_loop_results, _ = self.run_evaluation(test_mode=True)

        if len(eval_loop_results) == 0:
            return 1

        # remove the tensors from the eval results
        for i, result in enumerate(eval_loop_results):
            if isinstance(result, dict):
                for k, v in result.items():
                    if isinstance(v, torch.Tensor):
                        result[k] = v.cpu().item()

        return eval_loop_results

    def run_sanity_check(self, ref_model):
        using_val_step = ref_model.val_dataloader is not None and is_overridden('validation_step', ref_model)
        should_sanity_check = using_val_step and self.num_sanity_val_steps > 0 and self.limit_val_batches > 0

        # run tiny validation (if validation defined)
        # to make sure program won't crash during val
        if should_sanity_check:
            self.reset_val_dataloader(ref_model)
            self.num_sanity_val_batches = [
                min(self.num_sanity_val_steps, val_batches) for val_batches in self.num_val_batches
            ]

            # hook and callback
            self.running_sanity_check = True
            self.on_sanity_check_start()

            # run eval step
            _, eval_results = self.run_evaluation(test_mode=False, max_batches=self.num_sanity_val_batches)

            # allow no returns from eval
            if eval_results is not None and len(eval_results) > 0:
                # when we get a list back, used only the last item
                if isinstance(eval_results, list):
                    eval_results = eval_results[-1]

                if isinstance(eval_results, EvalResult):
                    callback_metrics = eval_results.callback_metrics
                else:
                    _, _, _, callback_metrics, _ = self.process_dict_result(eval_results)
                self.logger_connector.callback_metrics = callback_metrics

            self.on_sanity_check_end()
            self.running_sanity_check = False

    def test(
        self,
        model: Optional[LightningModule] = None,
        test_dataloaders: Optional[Union[DataLoader, List[DataLoader]]] = None,
        ckpt_path: Optional[str] = 'best',
        verbose: bool = True,
        datamodule: Optional[LightningDataModule] = None,
    ):
        r"""

        Separates from fit to make sure you never run on your test set until you want to.

        Args:
            ckpt_path: Either ``best`` or path to the checkpoint you wish to test.
                If ``None``, use the weights from the last epoch to test. Default to ``best``.

            datamodule: A instance of :class:`LightningDataModule`.

            model: The model to test.

            test_dataloaders: Either a single
                Pytorch Dataloader or a list of them, specifying validation samples.

            verbose: If True, prints the test results

        Returns:
            The final test result dictionary. If no test_epoch_end is defined returns a list of dictionaries
        """
        # --------------------
        # SETUP HOOK
        # --------------------
        self.verbose_test = verbose

        # If you supply a datamodule you can't supply train_dataloader or val_dataloaders
        if test_dataloaders and datamodule:
            raise MisconfigurationException(
                'You cannot pass test_dataloaders to trainer.test if you supply a datamodule'
            )

        # Attach datamodule to get setup/prepare_data added to model before the call to it below
        self.data_connector.attach_datamodule(model or self.get_model(), datamodule, 'test')

        if model is not None:
            results = self.__test_given_model(model, test_dataloaders)
        else:
            results = self.__test_using_best_weights(ckpt_path, test_dataloaders)

        self.teardown('test')

        return results

    def __test_using_best_weights(self, ckpt_path, test_dataloaders):
        model = self.get_model()

        # if user requests the best checkpoint but we don't have it, error
        if ckpt_path == 'best' and not self.checkpoint_callback.best_model_path:
            raise MisconfigurationException(
                'ckpt_path is "best", but ModelCheckpoint is not configured to save the best model.'
            )

        # load best weights
        if ckpt_path is not None:
            # ckpt_path is 'best' so load the best model
            if ckpt_path == 'best':
                ckpt_path = self.checkpoint_callback.best_model_path

            if len(ckpt_path) == 0:
                rank_zero_warn(
                    f'.test() found no path for the best weights, {ckpt_path}. Please '
                    f'specify a path for a checkpoint .test(ckpt_path=PATH)'
                )
                return {}
            if self.accelerator_backend is not None:
                self.accelerator_backend.barrier()

            ckpt = pl_load(ckpt_path, map_location=lambda storage, loc: storage)
            model.load_state_dict(ckpt['state_dict'])

        # attach dataloaders
        if test_dataloaders is not None:
            self.data_connector.attach_dataloaders(model, test_dataloaders=test_dataloaders)

        # run tests
        self.tested_ckpt_path = ckpt_path
        self.testing = True
        os.environ['PL_TESTING_MODE'] = '1'
        self.model = model
        results = self.fit(model)
        self.testing = False
        del os.environ['PL_TESTING_MODE']

        # teardown
        if self.is_function_implemented('teardown'):
            model_ref = self.get_model()
            model_ref.teardown('test')

        return results

    def __test_given_model(self, model, test_dataloaders):

        # attach data
        if test_dataloaders is not None:
            self.data_connector.attach_dataloaders(model, test_dataloaders=test_dataloaders)

        # run test
        # sets up testing so we short circuit to eval
        self.testing = True
        self.model = model
        results = self.fit(model)
        self.testing = False

        # teardown
        if self.is_function_implemented('teardown'):
            model.teardown('test')

        return results

    def call_setup_hook(self, model):
        # call setup after the ddp process has connected
        stage_name = 'test' if self.testing else 'fit'
        if self.datamodule is not None:
            called = self.datamodule.has_setup_test if self.testing else self.datamodule.has_setup_fit
            if not called:
                self.datamodule.setup(stage_name)
        self.setup(stage_name)
        model.setup(stage_name)

    def call_hook(self, hook_name, *args, **kwargs):
        # always profile hooks
        with self.profiler.profile(hook_name):

            # first call trainer hook
            if hasattr(self, hook_name):
                trainer_hook = getattr(self, hook_name)
                trainer_hook(*args, **kwargs)

            # next call hook in lightningModule
            output = None
            model_ref = self.get_model()
            if is_overridden(hook_name, model_ref):
                hook_fx = getattr(model_ref, hook_name)
                output = hook_fx(*args, **kwargs)

            # if the PL module doesn't have the hook then call the accelator
            # used to auto-reduce things for the user with Results obj
            elif hasattr(self.accelerator_backend, hook_name):
                accelerator_hook = getattr(self.accelerator_backend, hook_name)
                output = accelerator_hook(*args, **kwargs)

            return output