fairseq/tests/test_sequence_generator.py

# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import argparse
import tempfile
import unittest
import math
import numpy as np


import tests.utils as test_utils
import torch
from fairseq import search
from fairseq.data.dictionary import Dictionary
from fairseq.models.transformer import TransformerModel
from fairseq.sequence_generator import EnsembleModel, SequenceGenerator
from fairseq.ngram_repeat_block import NGramRepeatBlock
from fairseq.tasks.fairseq_task import LegacyFairseqTask


DEFAULT_TEST_VOCAB_SIZE = 100


class DummyTask(LegacyFairseqTask):
    def __init__(self, args):
        super().__init__(args)
        self.dictionary = get_dummy_dictionary()
        if getattr(self.args, "ctc", False):
            self.dictionary.add_symbol("<ctc_blank>")
        self.src_dict = self.dictionary
        self.tgt_dict = self.dictionary

    @property
    def source_dictionary(self):
        return self.src_dict

    @property
    def target_dictionary(self):
        return self.dictionary


def get_dummy_dictionary(vocab_size=DEFAULT_TEST_VOCAB_SIZE):
    dummy_dict = Dictionary()
    # add dummy symbol to satisfy vocab size
    for id, _ in enumerate(range(vocab_size)):
        dummy_dict.add_symbol("{}".format(id), n=1000)
    return dummy_dict


def get_dummy_task_and_parser():
    """
    to build a fariseq model, we need some dummy parse and task. This function
    is used to create dummy task and parser to faciliate model/criterion test

    Note: we use FbSpeechRecognitionTask as the dummy task. You may want
    to use other task by providing another function
    """
    parser = argparse.ArgumentParser(
        description="test_dummy_s2s_task", argument_default=argparse.SUPPRESS
    )
    DummyTask.add_args(parser)
    args = parser.parse_args([])
    task = DummyTask.setup_task(args)
    return task, parser


class TestJitSequenceGeneratorBase(unittest.TestCase):
    def setUp(self):
        self.task, self.parser = get_dummy_task_and_parser()
        eos = self.task.tgt_dict.eos()
        src_tokens = torch.randint(3, 50, (2, 10)).long()
        src_tokens = torch.cat((src_tokens, torch.LongTensor([[eos], [eos]])), -1)
        src_lengths = torch.LongTensor([2, 10])
        self.sample = {
            "net_input": {"src_tokens": src_tokens, "src_lengths": src_lengths}
        }
        TransformerModel.add_args(self.parser)
        args = self.parser.parse_args([])
        args.encoder_layers = 2
        args.decoder_layers = 1
        self.transformer_model = TransformerModel.build_model(args, self.task)

    def assertOutputEqual(self, hypo, pos_probs):
        pos_scores = torch.FloatTensor(pos_probs).log()
        self.assertTensorSizeEqual(hypo["positional_scores"], pos_scores)
        self.assertTensorSizeEqual(pos_scores.numel(), hypo["tokens"].numel())

    def assertTensorSizeEqual(self, t1, t2):
        self.assertEqual(t1.size(), t2.size(), "size mismatch")

    def assertAlmostEqual(self, t1, t2):
        self.assertEqual(t1.size(), t2.size(), "size mismatch")
        self.assertLess((t1 - t2).abs().max(), 1e-4)

    def assertTensorEqual(self, t1, t2):
        self.assertEqual(t1.size(), t2.size(), "size mismatch")
        self.assertEqual(t1.ne(t2).long().sum(), 0)

    def assertHypoEqual(self, h1, h2):
        "Check two hypos are equal"
        self.assertTensorEqual(h1["tokens"], h2["tokens"])
        self.assertAlmostEqual(h1["positional_scores"], h2["positional_scores"])
        self.assertLess(abs(h1["score"] - h2["score"]), 1e-6)
        self.assertAlmostEqual(h1["attention"], h2["attention"])

    def _test_save_and_load(self, scripted_module):
        with tempfile.NamedTemporaryFile() as f:
            scripted_module.save(f.name)
            torch.jit.load(f.name)


JIT_MSG = "Targeting OSS scriptability for the 1.6 release"


@unittest.skipIf(torch.__version__ < "1.6.0", JIT_MSG)
class TestJitSequenceGenerator(TestJitSequenceGeneratorBase):
    def test_export_transformer(self):
        model = self.transformer_model
        torch.jit.script(model)

    def test_ensemble_sequence_generator(self):
        model = self.transformer_model
        generator = SequenceGenerator(
            [model],
            self.task.tgt_dict,
            beam_size=2,
            no_repeat_ngram_size=2,
            max_len_b=10,
        )
        scripted_model = torch.jit.script(generator)
        self._test_save_and_load(scripted_model)

    def test_export_ensemble_model(self):
        model = self.transformer_model
        ensemble_models = EnsembleModel([model])
        torch.jit.script(ensemble_models)


class TestExportSearch(unittest.TestCase):
    def setUp(self):
        task, _ = get_dummy_task_and_parser()
        self.tgt_dict = task.tgt_dict
        self.min_top1_prob = 0.4

    def test_export_diverse_bs(self):
        search_strategy = search.DiverseBeamSearch(
            self.tgt_dict, num_groups=2, diversity_strength=0.0
        )
        torch.jit.script(search_strategy)

    def test_export_sampling(self):
        low_sampling_topp = self.min_top1_prob / 2.0
        search_strategy = search.Sampling(
            self.tgt_dict, sampling_topp=low_sampling_topp
        )
        torch.jit.script(search_strategy)

    def test_export_diverse_siblings_search(self):
        search_strategy = search.DiverseSiblingsSearch(
            self.tgt_dict, diversity_rate=0.5
        )
        torch.jit.script(search_strategy)


class TestSequenceGeneratorBase(unittest.TestCase):
    def assertHypoTokens(self, hypo, tokens):
        self.assertTensorEqual(hypo["tokens"], torch.LongTensor(tokens))

    def assertHypoScore(self, hypo, pos_probs, normalized=True, lenpen=1.0):
        pos_scores = torch.FloatTensor(pos_probs).log()
        self.assertAlmostEqual(hypo["positional_scores"], pos_scores)
        self.assertEqual(pos_scores.numel(), hypo["tokens"].numel())
        score = pos_scores.sum()
        if normalized:
            score /= pos_scores.numel() ** lenpen
        self.assertLess(abs(score - hypo["score"]), 1e-6)

    def assertAlmostEqual(self, t1, t2):
        self.assertEqual(t1.size(), t2.size(), "size mismatch")
        self.assertLess((t1 - t2).abs().max(), 1e-4)

    def assertTensorEqual(self, t1, t2):
        self.assertEqual(t1.size(), t2.size(), "size mismatch")
        self.assertEqual(t1.ne(t2).long().sum(), 0)


class TestSequenceGenerator(TestSequenceGeneratorBase):
    def setUp(self):
        (
            self.tgt_dict,
            self.w1,
            self.w2,
            src_tokens,
            src_lengths,
            self.model,
        ) = test_utils.sequence_generator_setup()
        self.sample = {
            "net_input": {"src_tokens": src_tokens, "src_lengths": src_lengths}
        }

    def test_with_normalization(self):
        generator = SequenceGenerator([self.model], self.tgt_dict, beam_size=2)
        hypos = generator.forward(self.sample)
        eos, w1, w2 = self.tgt_dict.eos(), self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, eos])
        self.assertHypoScore(hypos[0][0], [0.9, 1.0])
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w2, w1, w2, eos])
        self.assertHypoScore(hypos[0][1], [0.1, 0.9, 0.9, 1.0])
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w2, w1, eos])
        self.assertHypoScore(hypos[1][0], [0.7, 0.4, 0.4, 1.0])
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w1, w2, eos])
        self.assertHypoScore(hypos[1][1], [0.7, 0.4, 0.6])

    def test_without_normalization(self):
        # Sentence 1: unchanged from the normalized case
        # Sentence 2: beams swap order
        generator = SequenceGenerator(
            [self.model], self.tgt_dict, beam_size=2, normalize_scores=False
        )
        hypos = generator.forward(self.sample)
        eos, w1, w2 = self.tgt_dict.eos(), self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, eos])
        self.assertHypoScore(hypos[0][0], [0.9, 1.0], normalized=False)
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w2, w1, w2, eos])
        self.assertHypoScore(hypos[0][1], [0.1, 0.9, 0.9, 1.0], normalized=False)
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w2, eos])
        self.assertHypoScore(hypos[1][0], [0.7, 0.4, 0.6], normalized=False)
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w1, w2, w1, eos])
        self.assertHypoScore(hypos[1][1], [0.7, 0.4, 0.4, 1.0], normalized=False)

    def test_with_lenpen_favoring_short_hypos(self):
        lenpen = 0.6
        generator = SequenceGenerator(
            [self.model], self.tgt_dict, beam_size=2, len_penalty=lenpen
        )
        hypos = generator.forward(self.sample)
        eos, w1, w2 = self.tgt_dict.eos(), self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, eos])
        self.assertHypoScore(hypos[0][0], [0.9, 1.0], lenpen=lenpen)
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w2, w1, w2, eos])
        self.assertHypoScore(hypos[0][1], [0.1, 0.9, 0.9, 1.0], lenpen=lenpen)
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w2, eos])
        self.assertHypoScore(hypos[1][0], [0.7, 0.4, 0.6], lenpen=lenpen)
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w1, w2, w1, eos])
        self.assertHypoScore(hypos[1][1], [0.7, 0.4, 0.4, 1.0], lenpen=lenpen)

    def test_with_lenpen_favoring_long_hypos(self):
        lenpen = 5.0
        generator = SequenceGenerator(
            [self.model], self.tgt_dict, beam_size=2, len_penalty=lenpen
        )
        hypos = generator.forward(self.sample)
        eos, w1, w2 = self.tgt_dict.eos(), self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w2, w1, w2, eos])
        self.assertHypoScore(hypos[0][0], [0.1, 0.9, 0.9, 1.0], lenpen=lenpen)
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w1, eos])
        self.assertHypoScore(hypos[0][1], [0.9, 1.0], lenpen=lenpen)
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w2, w1, eos])
        self.assertHypoScore(hypos[1][0], [0.7, 0.4, 0.4, 1.0], lenpen=lenpen)
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w1, w2, eos])
        self.assertHypoScore(hypos[1][1], [0.7, 0.4, 0.6], lenpen=lenpen)

    def test_maxlen(self):
        generator = SequenceGenerator(
            [self.model], self.tgt_dict, beam_size=2, max_len_b=2
        )
        hypos = generator.forward(self.sample)
        eos, w1, w2 = self.tgt_dict.eos(), self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, eos])
        self.assertHypoScore(hypos[0][0], [0.9, 1.0])
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w2, w2, eos])
        self.assertHypoScore(hypos[0][1], [0.1, 0.1, 0.6])
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w2, eos])
        self.assertHypoScore(hypos[1][0], [0.7, 0.4, 0.6])
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w2, w2, eos])
        self.assertHypoScore(hypos[1][1], [0.3, 0.9, 0.01])

    def test_encoder_with_different_output_len(self):
        args = self.model.encoder.args
        task = test_utils.TestTranslationTask.setup_task(
            args, self.tgt_dict, self.tgt_dict
        )
        reshaping_model = test_utils.TestReshapingModel.build_model(args, task)
        generator = SequenceGenerator(
            [reshaping_model], self.tgt_dict, beam_size=2, max_len_b=2
        )
        hypos = generator.forward(self.sample)
        for sent in [0, 1]:
            for beam in [0, 1]:
                assert hypos[sent][beam]["attention"] is not None

    def test_generation_with_additional_input(self):
        args = self.model.encoder.args
        task = test_utils.TestTranslationTask.setup_task(
            args, self.tgt_dict, self.tgt_dict
        )
        add_input_model = test_utils.TestAdditionalInputModel.build_model(args, task)
        generator = SequenceGenerator([add_input_model], self.tgt_dict, beam_size=2)
        sample = self.sample.copy()
        sample["net_input"]["fancy_other_input"] = sample["net_input"]["src_tokens"]
        hypos = generator.forward(self.sample)
        eos, w1, w2 = self.tgt_dict.eos(), self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, eos])
        self.assertHypoScore(hypos[0][0], [0.9, 1.0])


@unittest.skipUnless(torch.cuda.is_available(), "")
class TestRepeatNgramBlocking(TestSequenceGeneratorBase):
    @classmethod
    def setUpClass(cls):
        (
            cls.tgt_dict,
            cls.w1,
            cls.w2,
            src_tokens,
            src_lengths,
            cls.model,
        ) = test_utils.sequence_generator_setup()
        return cls

    def test_finds_repetitive_tokens(self):
        bsz, vocab_size, beam_size, step = 2, 4, 1, 3
        generated_tok = torch.tensor(
            [[2, 2, 2, 2], [3, 3, 3, 3]], dtype=torch.long, device="cuda"
        )
        lprobs = torch.zeros((beam_size * bsz, vocab_size), device="cuda")
        desired_result = lprobs.new_tensor(
            [[0.0, 0.0, -math.inf, 0.0], [0.0, 0.0, 0.0, -math.inf]]
        )

        cuda_ext_result, baseline_result = self._compare_cuda_ext_to_default_implem(
            bsz, beam_size, generated_tok, lprobs, step, 2
        )
        self.assertTensorEqual(cuda_ext_result, desired_result)
        self.assertTensorEqual(baseline_result, desired_result)

    @unittest.skipIf(torch.__version__ < "1.6.0", JIT_MSG)
    def test_jit_no_extension(self):
        bsz, vocab_size, beam_size, step = 2, 4, 1, 3
        generated_tok = torch.tensor(
            [[2, 2, 2, 2], [3, 3, 3, 3]], dtype=torch.long, device="cuda"
        )
        lprobs = torch.zeros((beam_size * bsz, vocab_size), device="cuda")
        blocker = NGramRepeatBlock(2, use_extension=False)
        base_result = blocker(generated_tok, lprobs.clone(), bsz, beam_size, step)
        scripted_blocker = torch.jit.script(blocker)
        jit_result = scripted_blocker(
            generated_tok, lprobs.clone(), bsz, beam_size, step
        )
        self.assertTensorEqual(base_result, jit_result)

    def test_ngram_blocking_same_as_default_implem(self):
        """Test that cuda extension returns same things as default impl in many settings."""
        vocab_size = 4
        step = 6
        for _ in range(2):
            block_param = np.random.choice([1, 2, 3, 4])
            batch_size = np.random.randint(1, 8)
            beam_size = np.random.choice([1, 2, 4, 8])
            lprobs = torch.zeros((beam_size * batch_size, vocab_size), device="cuda")

            generated_tok = torch.tensor(
                np.random.randint(
                    0, vocab_size, size=(batch_size * beam_size, step + 1)
                ),
                device="cuda",
                dtype=torch.long,
            )
            self._compare_cuda_ext_to_default_implem(
                batch_size,
                beam_size,
                generated_tok,
                lprobs,
                step,
                block_param,
            )

    def _compare_cuda_ext_to_default_implem(
        self, bsz, beam_size, generated_tok, lprobs, step, block_param
    ):
        """Assert that cuda extension and default implem return the same thing."""
        blocker = NGramRepeatBlock(block_param)
        assert blocker.use_extension, "Extension not compiled"
        cuda_ext_result = blocker(
            generated_tok,
            lprobs.clone(),
            bsz,
            beam_size,
            step,
        )
        blocker.use_extension = False
        baseline_result = blocker(
            generated_tok,
            lprobs.clone(),
            bsz,
            beam_size,
            step,
        )
        self.assertTensorEqual(cuda_ext_result, baseline_result)
        blocker.use_extension = True
        return cuda_ext_result, baseline_result


class TestDiverseBeamSearch(TestSequenceGeneratorBase):
    def setUp(self):
        # construct dummy dictionary
        d = test_utils.dummy_dictionary(vocab_size=2)
        self.assertEqual(d.pad(), 1)
        self.assertEqual(d.eos(), 2)
        self.assertEqual(d.unk(), 3)
        self.eos = d.eos()
        self.w1 = 4
        self.w2 = 5

        # construct source data
        self.src_tokens = torch.LongTensor(
            [
                [self.w1, self.w2, self.eos],
                [self.w1, self.w2, self.eos],
            ]
        )
        self.src_lengths = torch.LongTensor([2, 2])

        args = argparse.Namespace()
        unk = 0.0
        args.beam_probs = [
            # step 0:
            torch.FloatTensor(
                [
                    # eos      w1   w2
                    # sentence 1:
                    [0.0, unk, 0.9, 0.1],  # beam 1
                    [0.0, unk, 0.9, 0.1],  # beam 2
                    # sentence 2:
                    [0.0, unk, 0.7, 0.3],
                    [0.0, unk, 0.7, 0.3],
                ]
            ),
            # step 1:
            torch.FloatTensor(
                [
                    # eos      w1   w2
                    # sentence 1:
                    [0.0, unk, 0.6, 0.4],
                    [0.0, unk, 0.6, 0.4],
                    # sentence 2:
                    [0.25, unk, 0.35, 0.4],
                    [0.25, unk, 0.35, 0.4],
                ]
            ),
            # step 2:
            torch.FloatTensor(
                [
                    # eos      w1   w2
                    # sentence 1:
                    [1.0, unk, 0.0, 0.0],
                    [1.0, unk, 0.0, 0.0],
                    # sentence 2:
                    [0.9, unk, 0.1, 0.0],
                    [0.9, unk, 0.1, 0.0],
                ]
            ),
        ]

        task = test_utils.TestTranslationTask.setup_task(args, d, d)
        self.model = task.build_model(args)
        self.tgt_dict = task.target_dictionary

    def test_diverse_beam_search(self):
        search_strategy = search.DiverseBeamSearch(
            self.tgt_dict, num_groups=2, diversity_strength=0.0
        )
        generator = SequenceGenerator(
            [self.model],
            self.tgt_dict,
            beam_size=2,
            search_strategy=search_strategy,
        )
        sample = {
            "net_input": {
                "src_tokens": self.src_tokens,
                "src_lengths": self.src_lengths,
            }
        }
        hypos = generator.forward(sample)
        eos, w1, w2 = self.eos, self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, w1, eos])
        self.assertHypoScore(hypos[0][0], [0.9, 0.6, 1.0])
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w1, w1, eos])
        self.assertHypoScore(hypos[0][1], [0.9, 0.6, 1.0])
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w2, eos])
        self.assertHypoScore(hypos[1][0], [0.7, 0.4, 0.9])
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w1, w2, eos])
        self.assertHypoScore(hypos[1][1], [0.7, 0.4, 0.9])


class TestDiverseSiblingsSearch(TestDiverseBeamSearch):
    def assertHypoScore(
        self, hypo, pos_probs, sibling_rank, diversity_rate, normalized=True, lenpen=1.0
    ):
        pos_scores = torch.FloatTensor(pos_probs).log()
        pos_scores.sub_(torch.Tensor(sibling_rank) * diversity_rate)
        self.assertAlmostEqual(hypo["positional_scores"], pos_scores)
        self.assertEqual(pos_scores.numel(), hypo["tokens"].numel())
        score = pos_scores.sum()
        if normalized:
            score /= pos_scores.numel() ** lenpen
        self.assertLess(abs(score - hypo["score"]), 1e-6)

    def test_diverse_beam_search(self):
        search_strategy = search.DiverseSiblingsSearch(
            self.tgt_dict, diversity_rate=0.5
        )
        generator = SequenceGenerator(
            [self.model], self.tgt_dict, beam_size=2, search_strategy=search_strategy
        )
        sample = {
            "net_input": {
                "src_tokens": self.src_tokens,
                "src_lengths": self.src_lengths,
            }
        }
        hypos = generator.forward(sample)
        eos, w1, w2 = self.eos, self.w1, self.w2
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, w1, eos])
        self.assertHypoScore(hypos[0][0], [0.9, 0.6, 1.0], [0, 1, 1], 0.5)
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w1, w2, eos])
        self.assertHypoScore(hypos[0][1], [0.9, 0.4, 1.0], [0, 2, 1], 0.5)
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w2, eos])
        self.assertHypoScore(hypos[1][0], [0.7, 0.4, 0.9], [0, 1, 1], 0.5)
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w1, w1, eos])
        self.assertHypoScore(hypos[1][1], [0.7, 0.35, 0.9], [0, 2, 1], 0.5)


class TestPrefixBeamSearch(TestSequenceGeneratorBase):
    def setUp(self):
        # construct dummy dictionary
        vocab_size = 10
        d = test_utils.dummy_dictionary(vocab_size=vocab_size)
        self.assertEqual(d.pad(), 1)
        self.assertEqual(d.eos(), 2)
        self.assertEqual(d.unk(), 3)
        self.eos = d.eos()
        self.w1 = 4
        self.w2 = 5
        self.beam_size = 3

        # construct prefix data
        self.tokens = torch.LongTensor(
            [
                [self.w1, self.w2, self.eos],
            ]
        )
        self.token_lengths = torch.LongTensor([2])

        args = argparse.Namespace()
        unk = 0.0
        args.beam_probs = [
            # prefix step 0:
            torch.FloatTensor(
                [
                    # eos      
                    [0.0, unk] + [1.0 / vocab_size] * vocab_size  # beam 1
                ] * self.beam_size
            ),
        ] * vocab_size

        task = test_utils.TestTranslationTask.setup_task(args, d, d)
        self.model = task.build_model(args)
        self.tgt_dict = task.target_dictionary

    def test_prefix_beam_search(self):
        search_strategy = search.BeamSearch(self.tgt_dict)
        generator = SequenceGenerator(
            [self.model],
            self.tgt_dict,
            beam_size=self.beam_size,
            search_strategy=search_strategy,
        )
        sample = {
            "net_input": {
                "src_tokens": self.tokens,
                "src_lengths": self.token_lengths,
            }
        }
        # make sure test sample doesn't break any assertion
        generator.forward(sample, prefix_tokens=self.tokens[:, :-1])

class TestTopPSamplingSearch(TestSequenceGeneratorBase):
    def setUp(self):
        # construct dummy dictionary
        d = test_utils.dummy_dictionary(vocab_size=2)
        self.assertEqual(d.pad(), 1)
        self.assertEqual(d.eos(), 2)
        self.assertEqual(d.unk(), 3)
        self.eos = d.eos()
        self.w1 = 4
        self.w2 = 5

        # construct source data
        self.src_tokens = torch.LongTensor(
            [
                [self.w1, self.w2, self.eos],
                [self.w1, self.w2, self.eos],
            ]
        )
        self.src_lengths = torch.LongTensor([2, 2])

        args = argparse.Namespace()
        unk = 0.0
        # The minimal probability of top 2 tokens.
        self.min_top2_prob = 0.75
        # The minimal probability of the top 1 token.
        self.min_top1_prob = 0.4

        w1_prob = self.min_top1_prob
        w2_prob = self.min_top2_prob - self.min_top1_prob
        eos_prob = 1 - self.min_top2_prob

        args.beam_probs = [
            # step 0:
            torch.FloatTensor(
                [
                    # eos      w1   w2
                    [0.0, unk, 1.0, 0.0],
                    [0.0, unk, 1.0, 0.0],
                    [0.0, unk, 1.0, 0.0],
                    [0.0, unk, 1.0, 0.0],
                ]
            ),
            # step 1:
            torch.FloatTensor(
                [
                    # eos           w1       w2
                    [eos_prob, unk, w1_prob, w2_prob],
                    [eos_prob, unk, w1_prob, w2_prob],
                    [eos_prob, unk, w1_prob, w2_prob],
                    [eos_prob, unk, w1_prob, w2_prob],
                ]
            ),
            # step 2:
            torch.FloatTensor(
                [
                    # eos      w1   w2
                    [1.0, unk, 0.0, 0.0],
                    [1.0, unk, 0.0, 0.0],
                    [1.0, unk, 0.0, 0.0],
                    [1.0, unk, 0.0, 0.0],
                ]
            ),
        ]

        task = test_utils.TestTranslationTask.setup_task(args, d, d)
        self.model = task.build_model(args)
        self.tgt_dict = task.target_dictionary

    def test_topp_sampling_search_low_prob(self):
        # Given a prob low enough to top-P sampling, we expect only the top
        # 1 token to be sampled, which always results in the same output.
        low_sampling_topp = self.min_top1_prob / 2.0
        search_strategy = search.Sampling(
            self.tgt_dict, sampling_topp=low_sampling_topp
        )
        generator = SequenceGenerator(
            [self.model], self.tgt_dict, beam_size=2, search_strategy=search_strategy
        )
        sample = {
            "net_input": {
                "src_tokens": self.src_tokens,
                "src_lengths": self.src_lengths,
            }
        }
        hypos = generator.forward(sample)
        eos, w1 = self.eos, self.w1
        # sentence 1, beam 1
        self.assertHypoTokens(hypos[0][0], [w1, w1, eos])
        self.assertHypoScore(hypos[0][0], [1.0, 0.4, 1.0])
        # sentence 1, beam 2
        self.assertHypoTokens(hypos[0][1], [w1, w1, eos])
        self.assertHypoScore(hypos[0][1], [1.0, 0.4, 1.0])
        # sentence 2, beam 1
        self.assertHypoTokens(hypos[1][0], [w1, w1, eos])
        self.assertHypoScore(hypos[1][0], [1.0, 0.4, 1.0])
        # sentence 2, beam 2
        self.assertHypoTokens(hypos[1][1], [w1, w1, eos])
        self.assertHypoScore(hypos[1][1], [1.0, 0.4, 1.0])

    def test_topp_sampling_search_high_prob(self):
        # Given a prob high enough to top-P sampling, any of the top 2
        # tokens could be sampled. This can cause different outputs.
        high_sampling_topp = (self.min_top1_prob + self.min_top2_prob) / 2.0
        search_strategy = search.Sampling(
            self.tgt_dict, sampling_topp=high_sampling_topp
        )
        generator = SequenceGenerator(
            [self.model], self.tgt_dict, beam_size=2, search_strategy=search_strategy
        )
        sample = {
            "net_input": {
                "src_tokens": self.src_tokens,
                "src_lengths": self.src_lengths,
            }
        }
        hypos = generator.forward(sample)
        eos, w1, w2 = self.eos, self.w1, self.w2
        # sentence 1, beam 1
        self.assertTrue(
            self.hypoTokens(hypos[0][0], [w1, w1, eos])
            or self.hypoTokens(hypos[0][0], [w1, w2, eos])
        )
        self.assertTrue(
            self.hypoScore(hypos[0][0], [1.0, 0.4, 1.0])
            or self.hypoScore(hypos[0][0], [1.0, 0.35, 1.0])
        )

        # sentence 1, beam 2
        self.assertTrue(
            self.hypoTokens(hypos[0][1], [w1, w1, eos])
            or self.hypoTokens(hypos[0][1], [w1, w2, eos])
        )
        self.assertTrue(
            self.hypoScore(hypos[0][1], [1.0, 0.4, 1.0])
            or self.hypoScore(hypos[0][1], [1.0, 0.35, 1.0])
        )

        # sentence 2, beam 1
        self.assertTrue(
            self.hypoTokens(hypos[1][0], [w1, w1, eos])
            or self.hypoTokens(hypos[1][0], [w1, w2, eos])
        )
        self.assertTrue(
            self.hypoScore(hypos[1][0], [1.0, 0.4, 1.0])
            or self.hypoScore(hypos[1][0], [1.0, 0.35, 1.0])
        )

        # sentence 2, beam 2
        self.assertTrue(
            self.hypoTokens(hypos[1][1], [w1, w1, eos])
            or self.hypoTokens(hypos[1][1], [w1, w2, eos])
        )
        self.assertTrue(
            self.hypoScore(hypos[1][1], [1.0, 0.4, 1.0])
            or self.hypoScore(hypos[1][1], [1.0, 0.35, 1.0])
        )

    def hypoTokens(self, hypo, tokens):
        return self.tensorEqual(hypo["tokens"], torch.LongTensor(tokens))

    def hypoScore(self, hypo, pos_probs, normalized=True, lenpen=1.0):
        pos_scores = torch.FloatTensor(pos_probs).log()
        if not self.almostEqual(hypo["positional_scores"], pos_scores):
            return False
        if pos_scores.numel() != hypo["tokens"].numel():
            return False
        score = pos_scores.sum()
        if normalized:
            score /= pos_scores.numel() ** lenpen
        return abs(score - hypo["score"]) < 1e-6

    def almostEqual(self, t1, t2):
        return t1.size() == t2.size() and (t1 - t2).abs().max() < 1e-4

    def tensorEqual(self, t1, t2):
        return t1.size() == t2.size() and t1.ne(t2).long().sum() == 0


if __name__ == "__main__":
    unittest.main()