githubmirror/oppia

scripts/build_test.py
1 301 строка57 KB
Shivkant Chauhan
[GSoC'23] M1.3.3 - Flags implementation in docker setup (#18644)
21 июл 2023, 08:21
21 июл 2023, 08:219ac3ef0
# coding: utf-8
#
# Copyright 2014 The Oppia Authors. All Rights Reserved.
#
# 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.

"""Unit tests for scripts/build.py."""

from __future__ import annotations

import ast
import collections
import contextlib
import io
import os
import re
import subprocess
import sys
import tempfile
import threading

from core import feconf
from core import utils
from core.tests import test_utils

from typing import ContextManager, Deque, Dict, Iterator, List, Tuple, Union

from . import build
from . import common
from . import install_python_dev_dependencies
from . import scripts_test_utils
from . import servers

TEST_DIR = os.path.join('core', 'tests', 'build', '')
TEST_SOURCE_DIR = os.path.join('core', 'tests', 'build_sources')

MOCK_ASSETS_DEV_DIR = os.path.join(TEST_SOURCE_DIR, 'assets', '')
MOCK_ASSETS_OUT_DIR = os.path.join(TEST_DIR, 'static', 'assets', '')
MOCK_EXTENSIONS_DEV_DIR = os.path.join(TEST_SOURCE_DIR, 'extensions', '')
MOCK_TEMPLATES_DEV_DIR = os.path.join(TEST_SOURCE_DIR, 'templates', '')

MOCK_TSC_OUTPUT_LOG_FILEPATH = os.path.join(
    TEST_SOURCE_DIR, 'mock_tsc_output_log.txt')
INVALID_FILENAME = 'invalid_filename.css'
INVALID_INPUT_FILEPATH = os.path.join(
    TEST_DIR, INVALID_FILENAME)
INVALID_OUTPUT_FILEPATH = os.path.join(
    TEST_DIR, INVALID_FILENAME)

EMPTY_DIR = os.path.join(TEST_DIR, 'empty', '')


def mock_managed_process(
    *unused_args: str, **unused_kwargs: str
) -> ContextManager[scripts_test_utils.PopenStub]:
    """Mock method for replacing the managed_process() functions.

    Returns:
        Context manager. A context manager that always yields a mock
        process.
    """
    return contextlib.nullcontext(
        enter_result=scripts_test_utils.PopenStub(alive=False))


class BuildTests(test_utils.GenericTestBase):
    """Test the build methods."""

    def tearDown(self) -> None:
        super().tearDown()
        build.safe_delete_directory_tree(TEST_DIR)
        build.safe_delete_directory_tree(EMPTY_DIR)

    def test_minify_func_with_invalid_filepath(self) -> None:
        """Tests minify_func with an invalid filepath."""
        with self.assertRaisesRegex(
            OSError, r'\[Errno 2\] No such file or directory:'
        ):
            build.minify_func(
                INVALID_INPUT_FILEPATH,
                INVALID_OUTPUT_FILEPATH,
                INVALID_FILENAME)

    def test_minify_and_create_sourcemap(self) -> None:
        """Tests _minify_and_create_sourcemap with an invalid filepath."""
        with self.assertRaisesRegex(
            subprocess.CalledProcessError,
            'returned non-zero exit status 1') as called_process:
            build._minify_and_create_sourcemap(  # pylint: disable=protected-access
                INVALID_INPUT_FILEPATH, INVALID_OUTPUT_FILEPATH)
        # Here we use MyPy ignore because the stubs of 'assertRaisesRegex' do
        # not contain any returncode attribute, so because of this MyPy throws
        # an '"Exception" has no attribute "returncode"' error. Thus to avoid
        # the error, we used ignore here.
        # `returncode` is the exit status of the child process.
        self.assertEqual(called_process.exception.returncode, 1)  # type: ignore[attr-defined]

    def test_minify_and_create_sourcemap_under_docker_environment(self) -> None:
        """Tests _minify_and_create_sourcemap with an invalid filepath."""
        with self.swap(feconf, 'OPPIA_IS_DOCKERIZED', True):
            build._minify_and_create_sourcemap(  # pylint: disable=protected-access
                INVALID_INPUT_FILEPATH, INVALID_OUTPUT_FILEPATH)

    def test_join_files(self) -> None:
        """Determine third_party.js contains the content of the first 10 JS
        files in /third_party/static.
        """
        third_party_js_stream = io.StringIO()
        # Get all filepaths from dependencies.json.
        dependency_filepaths = build.get_dependencies_filepaths()
        # Join and write all JS files in /third_party/static to file_stream.
        build._join_files(dependency_filepaths['js'], third_party_js_stream)  # pylint: disable=protected-access
        counter = 0
        # Only checking first 10 files.
        js_file_count = 10
        for js_filepath in dependency_filepaths['js']:
            if counter == js_file_count:
                break
            with utils.open_file(js_filepath, 'r') as js_file:
                # Assert that each line is copied over to file_stream object.
                for line in js_file:
                    self.assertIn(line, third_party_js_stream.getvalue())
            counter += 1

    def test_generate_copy_tasks_for_fonts(self) -> None:
        """Test _generate_copy_tasks_for_fonts ensures that the number of copy
        tasks matches the number of font files.
        """
        copy_tasks: Deque[threading.Thread] = collections.deque()
        # Get all filepaths from dependencies.json.
        dependency_filepaths = build.get_dependencies_filepaths()
        # Setup a sandbox folder for copying fonts.
        test_target = os.path.join('target', 'fonts', '')

        self.assertEqual(len(copy_tasks), 0)
        copy_tasks += build._generate_copy_tasks_for_fonts(  # pylint: disable=protected-access
            dependency_filepaths['fonts'], test_target)
        # Asserting the same number of copy tasks and number of font files.
        self.assertEqual(len(copy_tasks), len(dependency_filepaths['fonts']))

    def test_insert_hash(self) -> None:
        """Test _insert_hash returns correct filenames with provided hashes."""
        self.assertEqual(
            build._insert_hash('file.js', '123456'), 'file.123456.js')  # pylint: disable=protected-access
        self.assertEqual(
            build._insert_hash(  # pylint: disable=protected-access
                'path/to/file.js', '654321'), 'path/to/file.654321.js')
        self.assertEqual(
            build._insert_hash('file.min.js', 'abcdef'), 'file.min.abcdef.js')  # pylint: disable=protected-access
        self.assertEqual(
            build._insert_hash(  # pylint: disable=protected-access
                'path/to/file.min.js', 'fedcba'), 'path/to/file.min.fedcba.js')

    def test_get_file_count(self) -> None:
        """Test get_file_count returns the correct number of files, excluding
        file with extensions in FILE_EXTENSIONS_TO_IGNORE and files that should
        not be built.
        """
        all_inclusive_file_count = 0
        for _, _, files in os.walk(MOCK_EXTENSIONS_DEV_DIR):
            all_inclusive_file_count += len(files)
        ignored_file_count = 0
        for _, _, files in os.walk(MOCK_EXTENSIONS_DEV_DIR):
            for filename in files:
                if not build.should_file_be_built(filename) or any(
                        filename.endswith(p)
                        for p in build.FILE_EXTENSIONS_TO_IGNORE):
                    ignored_file_count += 1
        self.assertEqual(
            all_inclusive_file_count - ignored_file_count,
            build.get_file_count(MOCK_EXTENSIONS_DEV_DIR))

    def test_compare_file_count(self) -> None:
        """Test _compare_file_count raises exception when there is a
        mismatched file count between 2 dirs list.
        """

        # Test when both lists contain single directory.
        build.ensure_directory_exists(EMPTY_DIR)
        source_dir_file_count = build.get_file_count(EMPTY_DIR)
        assert source_dir_file_count == 0
        target_dir_file_count = build.get_file_count(MOCK_ASSETS_DEV_DIR)
        # Ensure that ASSETS_DEV_DIR has at least 1 file.
        assert target_dir_file_count > 0
        with self.assertRaisesRegex(
            ValueError, (
                '%s files in first dir list != %s files in second dir list') %
            (source_dir_file_count, target_dir_file_count)):
            build._compare_file_count([EMPTY_DIR], [MOCK_ASSETS_DEV_DIR])  # pylint: disable=protected-access

        # Test when one of the lists contain multiple directories.
        mock_extensions_dir_list = [MOCK_EXTENSIONS_DEV_DIR]
        target_dir_file_count = build.get_file_count(MOCK_EXTENSIONS_DEV_DIR)

        # Ensure that MOCK_EXTENSIONS_DIR has at least 1 file.
        assert target_dir_file_count > 0
        with self.assertRaisesRegex(
            ValueError, (
                '%s files in first dir list != %s files in second dir list') %
            (source_dir_file_count, target_dir_file_count)):
            build._compare_file_count([EMPTY_DIR], mock_extensions_dir_list)  # pylint: disable=protected-access

        # Reset EMPTY_DIRECTORY to clean state.
        build.safe_delete_directory_tree(EMPTY_DIR)

    def test_verify_filepath_hash(self) -> None:
        """Test _verify_filepath_hash raises exception:
            1) When there is an empty hash dict.
            2) When a filename is expected to contain hash but does not.
            3) When there is a hash in filename that cannot be found in
                hash dict.
        """
        # Final filepath example: base.240933e7564bd72a4dde42ee23260c5f.html.
        file_hashes: Dict[str, str] = {}
        base_filename = 'base.html'
        with self.assertRaisesRegex(ValueError, 'Hash dict is empty'):
            build._verify_filepath_hash(base_filename, file_hashes)  # pylint: disable=protected-access

        # Generate a random hash dict for base.html.
        file_hashes = {base_filename: (
            test_utils.generate_random_hexa_str())}
        with self.assertRaisesRegex(
            ValueError, '%s is expected to contain MD5 hash' % base_filename):
            build._verify_filepath_hash(base_filename, file_hashes)  # pylint: disable=protected-access

        base_without_hash_filename = 'base_without_hash.html'
        build._verify_filepath_hash(  # pylint: disable=protected-access
            base_without_hash_filename, file_hashes)

        bad_filepath = 'README'
        with self.assertRaisesRegex(
            ValueError, 'Filepath has less than 2 partitions after splitting'):
            build._verify_filepath_hash(bad_filepath, file_hashes)  # pylint: disable=protected-access

        hashed_base_filename = build._insert_hash(  # pylint: disable=protected-access
            base_filename, test_utils.generate_random_hexa_str())
        with self.assertRaisesRegex(
            KeyError,
            'Hash from file named %s does not match hash dict values' %
            hashed_base_filename):
            build._verify_filepath_hash(hashed_base_filename, file_hashes)  # pylint: disable=protected-access

    def test_process_html(self) -> None:
        """Test process_html removes whitespaces."""
        base_html_source_path = (
            os.path.join(MOCK_TEMPLATES_DEV_DIR, 'base.html'))

        build._ensure_files_exist([base_html_source_path])  # pylint: disable=protected-access
        minified_html_file_stream = io.StringIO()

        # Assert that base.html has white spaces and has original filepaths.
        with utils.open_file(
            base_html_source_path, 'r') as source_base_file:
            source_base_file_content = source_base_file.read()
            self.assertRegex(
                source_base_file_content, r'\s{2,}',
                msg='No white spaces detected in %s unexpectedly'
                % base_html_source_path)

        # Build base.html file.
        with utils.open_file(
            base_html_source_path, 'r') as source_base_file:
            build.process_html(source_base_file, minified_html_file_stream)

        minified_html_file_content = minified_html_file_stream.getvalue()
        self.assertNotRegex(
            minified_html_file_content, r'\s{2,}',
            msg='All white spaces must be removed from %s' %
            base_html_source_path)

    def test_should_file_be_built(self) -> None:
        """Test should_file_be_built returns the correct boolean value for
        filepath that should be built.
        """
        service_ts_filepath = os.path.join('core', 'pages', 'AudioService.ts')
        spec_js_filepath = os.path.join('core', 'pages', 'AudioServiceSpec.js')
        webdriverio_filepath = os.path.join('extensions', 'webdriverio.js')

        python_controller_filepath = os.path.join('base.py')
        pyc_test_filepath = os.path.join(
            'core', 'controllers', 'base.pyc')
        python_test_filepath = os.path.join(
            'core', 'tests', 'base_test.py')

        self.assertFalse(build.should_file_be_built(spec_js_filepath))
        self.assertFalse(build.should_file_be_built(webdriverio_filepath))

        self.assertFalse(build.should_file_be_built(service_ts_filepath))

        self.assertFalse(build.should_file_be_built(python_test_filepath))
        self.assertFalse(build.should_file_be_built(pyc_test_filepath))
        self.assertTrue(build.should_file_be_built(python_controller_filepath))

        # Swapping out constants to check if the reverse is true.
        # ALL JS files that ends with ...Service.js should not be built.
        with self.swap(
            build, 'JS_FILENAME_SUFFIXES_TO_IGNORE', ('Service.js',)
        ):
            self.assertTrue(build.should_file_be_built(spec_js_filepath))

    def test_hash_should_be_inserted(self) -> None:
        """Test hash_should_be_inserted returns the correct boolean value
        for filepath that should be hashed.
        """
        with self.swap(
            build, 'FILEPATHS_NOT_TO_RENAME', (
                '*.py', 'path/to/fonts/*', 'path/to/third_party.min.js.map',
                'path/to/third_party.min.css.map')
        ):
            self.assertFalse(build.hash_should_be_inserted(
                'path/to/fonts/fontawesome-webfont.svg'))
            self.assertFalse(build.hash_should_be_inserted(
                'path/to/third_party.min.css.map'))
            self.assertFalse(build.hash_should_be_inserted(
                'path/to/third_party.min.js.map'))
            self.assertTrue(build.hash_should_be_inserted(
                'path/to/wrongFonts/fonta.eot'))
            self.assertTrue(build.hash_should_be_inserted(
                'rich_text_components/Video/protractor.js'))
            self.assertFalse(build.hash_should_be_inserted(
                'main.py'))
            self.assertFalse(build.hash_should_be_inserted(
                'extensions/domain.py'))

    def test_generate_copy_tasks_to_copy_from_source_to_target(self) -> None:
        """Test generate_copy_tasks_to_copy_from_source_to_target queues up
        the same number of copy tasks as the number of files in the directory.
        """
        assets_hashes = build.get_file_hashes(MOCK_ASSETS_DEV_DIR)
        total_file_count = build.get_file_count(MOCK_ASSETS_DEV_DIR)
        copy_tasks: Deque[threading.Thread] = collections.deque()

        self.assertEqual(len(copy_tasks), 0)
        copy_tasks += build.generate_copy_tasks_to_copy_from_source_to_target(
            MOCK_ASSETS_DEV_DIR, MOCK_ASSETS_OUT_DIR, assets_hashes)
        self.assertEqual(len(copy_tasks), total_file_count)

    def test_is_file_hash_provided_to_frontend(self) -> None:
        """Test is_file_hash_provided_to_frontend returns the correct boolean
        value for filepath that should be provided to frontend.
        """
        with self.swap(
            build, 'FILEPATHS_PROVIDED_TO_FRONTEND',
            ('path/to/file.js', 'path/to/file.html', 'file.js')
        ):
            self.assertTrue(
                build.is_file_hash_provided_to_frontend('path/to/file.js'))
            self.assertTrue(
                build.is_file_hash_provided_to_frontend('path/to/file.html'))
            self.assertTrue(build.is_file_hash_provided_to_frontend('file.js'))
        with self.swap(
            build, 'FILEPATHS_PROVIDED_TO_FRONTEND',
            ('path/to/*', '*.js', '*_end.html')
        ):
            self.assertTrue(
                build.is_file_hash_provided_to_frontend('path/to/file.js'))
            self.assertTrue(
                build.is_file_hash_provided_to_frontend('path/to/file.html'))
            self.assertTrue(build.is_file_hash_provided_to_frontend('file.js'))
            self.assertFalse(
                build.is_file_hash_provided_to_frontend('path/file.css'))
            self.assertTrue(
                build.is_file_hash_provided_to_frontend('good_end.html'))
            self.assertFalse(
                build.is_file_hash_provided_to_frontend('bad_end.css'))

    def test_get_filepaths_by_extensions(self) -> None:
        """Test get_filepaths_by_extensions only returns filepaths in
        directory with given extensions.
        """
        filepaths: List[str] = []
        build.ensure_directory_exists(MOCK_ASSETS_DEV_DIR)
        extensions: Tuple[str, ...] = ('.json', '.svg',)

        self.assertEqual(len(filepaths), 0)
        filepaths = build.get_filepaths_by_extensions(
            MOCK_ASSETS_DEV_DIR, extensions)
        for filepath in filepaths:
            self.assertTrue(any(filepath.endswith(p) for p in extensions))
        file_count = 0
        for _, _, filenames in os.walk(MOCK_ASSETS_DEV_DIR):
            for filename in filenames:
                if any(filename.endswith(p) for p in extensions):
                    file_count += 1
        self.assertEqual(len(filepaths), file_count)

        filepaths = []
        extensions = ('.pdf', '.viminfo', '.idea',)

        self.assertEqual(len(filepaths), 0)
        filepaths = build.get_filepaths_by_extensions(
            MOCK_ASSETS_DEV_DIR, extensions)
        self.assertEqual(len(filepaths), 0)

    def test_get_file_hashes(self) -> None:
        """Test get_file_hashes gets hashes of all files in directory,
        excluding file with extensions in FILE_EXTENSIONS_TO_IGNORE.
        """
        # Prevent getting hashes of HTML files.
        with self.swap(build, 'FILE_EXTENSIONS_TO_IGNORE', ('.html',)):
            file_hashes: Dict[str, str] = {}
            self.assertEqual(len(file_hashes), 0)
            file_hashes = build.get_file_hashes(MOCK_EXTENSIONS_DEV_DIR)
            self.assertGreater(len(file_hashes), 0)
            # Assert that each hash's filepath exists and does not include files
            # with extensions in FILE_EXTENSIONS_TO_IGNORE.
            for filepath in file_hashes:
                abs_filepath = os.path.join(MOCK_EXTENSIONS_DEV_DIR, filepath)
                self.assertTrue(os.path.isfile(abs_filepath))
                self.assertFalse(filepath.endswith('.html'))

    def test_filter_hashes(self) -> None:
        """Test filter_hashes filters the provided hash correctly."""
        # Set constant to provide everything to frontend.
        with self.swap(build, 'FILEPATHS_PROVIDED_TO_FRONTEND', ('*',)):
            hashes = {'path/to/file.js': '123456',
                      'path/file.min.js': '123456'}
            filtered_hashes = build.filter_hashes(hashes)
            self.assertEqual(
                filtered_hashes['/path/to/file.js'],
                hashes['path/to/file.js'])
            self.assertEqual(
                filtered_hashes['/path/file.min.js'],
                hashes['path/file.min.js'])

        with self.swap(
            build, 'FILEPATHS_PROVIDED_TO_FRONTEND',
            ('test_path/*', 'path/to/file.js')
        ):
            hashes = {'path/to/file.js': '123456',
                      'test_path/to/file.html': '123456',
                      'test_path/to/file.js': 'abcdef',
                      'path/path/file.js': 'zyx123',
                      'file.html': '321xyz'}
            filtered_hashes = build.filter_hashes(hashes)
            self.assertIn('/path/to/file.js', filtered_hashes)
            self.assertIn('/test_path/to/file.html', filtered_hashes)
            self.assertIn('/test_path/to/file.js', filtered_hashes)
            self.assertNotIn('/path/path/file.js', filtered_hashes)
            self.assertNotIn('/file.html', filtered_hashes)

    def test_save_hashes_to_file(self) -> None:
        """Test save_hashes_to_file saves provided hash dict correctly to
        JSON file.
        """
        hashes_path = os.path.join(MOCK_ASSETS_OUT_DIR, 'hashes.json')

        # Set constant to provide everything to frontend.
        with self.swap(build, 'FILEPATHS_PROVIDED_TO_FRONTEND', ('*',)):
            with self.swap(build, 'HASHES_JSON_FILEPATH', hashes_path):
                hashes = {'path/file.js': '123456'}
                build.save_hashes_to_file(hashes)
                with utils.open_file(hashes_path, 'r') as hashes_file:
                    self.assertEqual(
                        hashes_file.read(), '{"/path/file.js": "123456"}\n')

                hashes = {'file.js': '123456', 'file.min.js': '654321'}
                build.save_hashes_to_file(hashes)
                with utils.open_file(hashes_path, 'r') as hashes_file:
                    self.assertEqual(
                        ast.literal_eval(hashes_file.read()),
                        {'/file.min.js': '654321', '/file.js': '123456'})
                os.remove(hashes_path)

    def test_execute_tasks(self) -> None:
        """Test _execute_tasks joins all threads after executing all tasks."""
        build_tasks: Deque[threading.Thread] = collections.deque()
        build_thread_names: List[Union[threading.Thread, str]] = []
        task_count = 2
        count = task_count
        while count:
            thread_name = 'Build-test-thread-%s' % count
            build_thread_names.append(thread_name)
            task = threading.Thread(
                name=thread_name,
                target=build.minify_func,
                args=(
                    INVALID_INPUT_FILEPATH,
                    INVALID_OUTPUT_FILEPATH,
                    INVALID_FILENAME))
            build_tasks.append(task)
            count -= 1

        extra_build_threads = [
            thread.name for thread in threading.enumerate()
            if thread in build_thread_names]
        self.assertEqual(len(extra_build_threads), 0)
        build._execute_tasks(build_tasks)  # pylint: disable=protected-access
        with self.assertRaisesRegex(
            OSError, 'threads can only be started once'):
            build._execute_tasks(build_tasks)  # pylint: disable=protected-access
        # Assert that all threads are joined.
        extra_build_threads = [
            thread.name for thread in threading.enumerate()
            if thread in build_thread_names]
        self.assertEqual(len(extra_build_threads), 0)

    def test_generate_build_tasks_to_build_all_files_in_directory(self) -> None:
        """Test generate_build_tasks_to_build_all_files_in_directory queues up
        the same number of build tasks as the number of files in the source
        directory.
        """
        tasks: Deque[threading.Thread] = collections.deque()

        self.assertEqual(len(tasks), 0)
        # Build all files.
        tasks = build.generate_build_tasks_to_build_all_files_in_directory(
            MOCK_ASSETS_DEV_DIR, MOCK_ASSETS_OUT_DIR)
        total_file_count = build.get_file_count(MOCK_ASSETS_DEV_DIR)
        self.assertEqual(len(tasks), total_file_count)

    def test_generate_build_tasks_to_build_files_from_filepaths(self) -> None:
        """Test generate_build_tasks_to_build_files_from_filepaths queues up a
        corresponding number of build tasks to the number of file changes.
        """
        new_filename = 'dependencies.json'
        recently_changed_filenames = [
            os.path.join(MOCK_ASSETS_DEV_DIR, new_filename)]
        build_tasks: Deque[threading.Thread] = collections.deque()

        self.assertEqual(len(build_tasks), 0)
        build_tasks += build.generate_build_tasks_to_build_files_from_filepaths(
            MOCK_ASSETS_DEV_DIR, MOCK_ASSETS_OUT_DIR,
            recently_changed_filenames)
        self.assertEqual(len(build_tasks), len(recently_changed_filenames))

        build_tasks.clear()
        svg_filepaths = build.get_filepaths_by_extensions(
            MOCK_ASSETS_DEV_DIR, ('.svg',))
        # Make sure there is at least 1 SVG file.
        self.assertGreater(len(svg_filepaths), 0)

        self.assertEqual(len(build_tasks), 0)
        build_tasks += build.generate_build_tasks_to_build_files_from_filepaths(
            MOCK_ASSETS_DEV_DIR, MOCK_ASSETS_OUT_DIR, svg_filepaths)
        self.assertEqual(len(build_tasks), len(svg_filepaths))

    def test_generate_build_tasks_to_build_directory(self) -> None:
        """Test generate_build_tasks_to_build_directory queues up a
        corresponding number of build tasks according to the given scenario.
        """
        extensions_dirnames_to_dirpaths = {
            'dev_dir': MOCK_EXTENSIONS_DEV_DIR,
            'staging_dir': os.path.join(
                TEST_DIR, 'backend_prod_files', 'extensions', ''),
            'out_dir': os.path.join(TEST_DIR, 'build', 'extensions', '')
        }
        file_hashes = build.get_file_hashes(MOCK_EXTENSIONS_DEV_DIR)
        build_dir_tasks: Deque[threading.Thread] = collections.deque()
        build_all_files_tasks = (
            build.generate_build_tasks_to_build_all_files_in_directory(
                MOCK_EXTENSIONS_DEV_DIR,
                extensions_dirnames_to_dirpaths['out_dir']))
        self.assertGreater(len(build_all_files_tasks), 0)

        # Test for building all files when staging dir does not exist.
        self.assertEqual(len(build_dir_tasks), 0)
        build_dir_tasks += build.generate_build_tasks_to_build_directory(
            extensions_dirnames_to_dirpaths)
        self.assertEqual(len(build_dir_tasks), len(build_all_files_tasks))

        build.safe_delete_directory_tree(TEST_DIR)
        build_dir_tasks.clear()

        # Test for building only new files when staging dir exists.
        build.ensure_directory_exists(
            extensions_dirnames_to_dirpaths['staging_dir'])
        self.assertEqual(len(build_dir_tasks), 0)

        build_dir_tasks += build.generate_build_tasks_to_build_directory(
            extensions_dirnames_to_dirpaths)
        self.assertEqual(len(build_dir_tasks), len(build_all_files_tasks))

        build.safe_delete_directory_tree(TEST_DIR)

        # Build all files and save to final directory.
        build.ensure_directory_exists(
            extensions_dirnames_to_dirpaths['staging_dir'])
        build._execute_tasks(build_dir_tasks)  # pylint: disable=protected-access
        self.assertEqual(threading.active_count(), 1)
        build._execute_tasks(  # pylint: disable=protected-access
            build.generate_copy_tasks_to_copy_from_source_to_target(
                extensions_dirnames_to_dirpaths['staging_dir'],
                extensions_dirnames_to_dirpaths['out_dir'], file_hashes))

        build_dir_tasks.clear()

        # Test for only building files that need to be rebuilt.
        self.assertEqual(len(build_dir_tasks), 0)
        build_dir_tasks += build.generate_build_tasks_to_build_directory(
            extensions_dirnames_to_dirpaths)
        file_extensions_to_always_rebuild = ('.html', '.py',)
        always_rebuilt_filepaths = build.get_filepaths_by_extensions(
            MOCK_EXTENSIONS_DEV_DIR, file_extensions_to_always_rebuild)
        self.assertGreater(len(always_rebuilt_filepaths), 0)
        self.assertEqual(len(build_dir_tasks), len(always_rebuilt_filepaths))

        build.safe_delete_directory_tree(TEST_DIR)

    def test_re_build_recently_changed_files_at_dev_dir(self) -> None:
        temp_file = tempfile.NamedTemporaryFile()
        temp_file_name = '%ssome_file.js' % MOCK_EXTENSIONS_DEV_DIR
        # Here MyPy assumes that the 'name' attribute is read-only. In order to
        # silence the MyPy complaints `setattr` is used to set the attribute.
        setattr(temp_file, 'name', temp_file_name)
        with utils.open_file(
            '%ssome_file.js' % MOCK_EXTENSIONS_DEV_DIR, 'w') as tmp:
            tmp.write(u'Some content.')

        extensions_dirnames_to_dirpaths = {
            'dev_dir': MOCK_EXTENSIONS_DEV_DIR,
            'staging_dir': os.path.join(
                TEST_DIR, 'backend_prod_files', 'extensions', ''),
            'out_dir': os.path.join(TEST_DIR, 'build', 'extensions', '')
        }

        build_dir_tasks: Deque[threading.Thread] = collections.deque()
        build_all_files_tasks = (
            build.generate_build_tasks_to_build_all_files_in_directory(
                MOCK_EXTENSIONS_DEV_DIR,
                extensions_dirnames_to_dirpaths['out_dir']))
        self.assertGreater(len(build_all_files_tasks), 0)

        # Test for building all files when staging dir does not exist.
        self.assertEqual(len(build_dir_tasks), 0)
        build_dir_tasks += build.generate_build_tasks_to_build_directory(
            extensions_dirnames_to_dirpaths)
        self.assertEqual(len(build_dir_tasks), len(build_all_files_tasks))

        build.safe_delete_directory_tree(TEST_DIR)
        build_dir_tasks.clear()

        # Test for building only new files when staging dir exists.
        build.ensure_directory_exists(
            extensions_dirnames_to_dirpaths['staging_dir'])
        self.assertEqual(len(build_dir_tasks), 0)

        build_dir_tasks = build.generate_build_tasks_to_build_directory(
            extensions_dirnames_to_dirpaths)
        file_extensions_to_always_rebuild = ('.py', '.js', '.html')
        always_rebuilt_filepaths = build.get_filepaths_by_extensions(
            MOCK_EXTENSIONS_DEV_DIR, file_extensions_to_always_rebuild)
        self.assertEqual(
            sorted(always_rebuilt_filepaths), sorted(
                ['base.py', 'CodeRepl.py', '__init__.py', 'some_file.js',
                 'DragAndDropSortInput.py', 'code_repl_prediction.html']))
        self.assertGreater(len(always_rebuilt_filepaths), 0)

        # Test that 'some_file.js' is not rebuilt, i.e it is built for the first
        # time.
        self.assertEqual(len(build_dir_tasks), len(always_rebuilt_filepaths))
        self.assertIn('some_file.js', always_rebuilt_filepaths)
        self.assertNotIn('some_file.js', build_dir_tasks)

        build.safe_delete_directory_tree(TEST_DIR)
        temp_file.close()

        if os.path.isfile(temp_file_name):
            # On Windows system, occasionally this temp file is not deleted.
            os.remove(temp_file_name)

    def test_get_recently_changed_filenames(self) -> None:
        """Test get_recently_changed_filenames detects file recently added."""
        # Create an empty folder.
        build.ensure_directory_exists(EMPTY_DIR)
        # Get hashes from ASSETS_DEV_DIR to simulate a folder with built files.
        assets_hashes = build.get_file_hashes(MOCK_ASSETS_DEV_DIR)
        recently_changed_filenames: List[str] = []

        self.assertEqual(len(recently_changed_filenames), 0)
        recently_changed_filenames = build.get_recently_changed_filenames(
            assets_hashes, EMPTY_DIR)
        # Since all HTML and Python files are already built, they are ignored.
        with self.swap(build, 'FILE_EXTENSIONS_TO_IGNORE', ('.html', '.py',)):
            self.assertEqual(
                len(recently_changed_filenames), build.get_file_count(
                    MOCK_ASSETS_DEV_DIR))

        build.safe_delete_directory_tree(EMPTY_DIR)

    def test_generate_delete_tasks_to_remove_deleted_files(self) -> None:
        """Test generate_delete_tasks_to_remove_deleted_files queues up the
        same number of deletion task as the number of deleted files.
        """
        delete_tasks: Deque[threading.Thread] = collections.deque()
        # The empty dict means that all files should be removed.
        file_hashes: Dict[str, str] = {}

        self.assertEqual(len(delete_tasks), 0)
        delete_tasks += build.generate_delete_tasks_to_remove_deleted_files(
            file_hashes, MOCK_TEMPLATES_DEV_DIR)
        self.assertEqual(
            len(delete_tasks), build.get_file_count(MOCK_TEMPLATES_DEV_DIR))

    def test_generate_app_yaml_with_deploy_mode(self) -> None:
        mock_dev_yaml_filepath = 'mock_app_dev.yaml'
        mock_yaml_filepath = 'mock_app.yaml'
        app_dev_yaml_filepath_swap = self.swap(
            build, 'APP_DEV_YAML_FILEPATH', mock_dev_yaml_filepath)
        app_yaml_filepath_swap = self.swap(
            build, 'APP_YAML_FILEPATH', mock_yaml_filepath)
        env_vars_to_remove_from_deployed_app_yaml_swap = self.swap(
            build,
            'ENV_VARS_TO_REMOVE_FROM_DEPLOYED_APP_YAML',
            ['FIREBASE_AUTH_EMULATOR_HOST']
        )

        app_dev_yaml_temp_file = tempfile.NamedTemporaryFile()
        # Here MyPy assumes that the 'name' attribute is read-only. In order to
        # silence the MyPy complaints `setattr` is used to set the attribute.
        setattr(
            app_dev_yaml_temp_file, 'name', mock_dev_yaml_filepath)
        with utils.open_file(mock_dev_yaml_filepath, 'w') as tmp:
            with self.swap(feconf, 'OPPIA_IS_DOCKERIZED', True):
                tmp.write('Some content in mock_app_dev.yaml\n')
                tmp.write(
                    '  FIREBASE_AUTH_EMULATOR_HOST: "firebase:9099"\n')
                tmp.write('version: default')

        app_yaml_temp_file = tempfile.NamedTemporaryFile()
        # Here MyPy assumes that the 'name' attribute is read-only. In order to
        # silence the MyPy complaints `setattr` is used to set the attribute.
        setattr(app_yaml_temp_file, 'name', mock_yaml_filepath)
        with utils.open_file(mock_yaml_filepath, 'w') as tmp:
            tmp.write(u'Initial content in mock_app.yaml')

        with app_dev_yaml_filepath_swap, app_yaml_filepath_swap:
            with env_vars_to_remove_from_deployed_app_yaml_swap:
                build.generate_app_yaml(deploy_mode=True)

        with utils.open_file(mock_yaml_filepath, 'r') as yaml_file:
            content = yaml_file.read()

        self.assertEqual(
            content,
            '# THIS FILE IS AUTOGENERATED, DO NOT MODIFY\n'
            'Some content in mock_app_dev.yaml\n')

        app_yaml_temp_file.close()
        app_dev_yaml_temp_file.close()

    def test_generate_app_yaml_with_deploy_mode_with_nonexistent_var_raises(
        self
    ) -> None:
        mock_dev_yaml_filepath = 'mock_app_dev.yaml'
        mock_yaml_filepath = 'mock_app.yaml'
        app_dev_yaml_filepath_swap = self.swap(
            build, 'APP_DEV_YAML_FILEPATH', mock_dev_yaml_filepath)
        app_yaml_filepath_swap = self.swap(
            build, 'APP_YAML_FILEPATH', mock_yaml_filepath)
        env_vars_to_remove_from_deployed_app_yaml_swap = self.swap(
            build,
            'ENV_VARS_TO_REMOVE_FROM_DEPLOYED_APP_YAML',
            ['DATASTORE_HOST']
        )

        app_dev_yaml_temp_file = tempfile.NamedTemporaryFile()
        # Here MyPy assumes that the 'name' attribute is read-only. In order to
        # silence the MyPy complaints `setattr` is used to set the attribute.
        setattr(
            app_dev_yaml_temp_file, 'name', mock_dev_yaml_filepath)
        # TODO(#18260): Change this when we permanently move to
        # the Dockerized Setup.
        firebase_host = (
            'firebase' if feconf.OPPIA_IS_DOCKERIZED else 'localhost'
        )
        with utils.open_file(mock_dev_yaml_filepath, 'w') as tmp:
            tmp.write('Some content in mock_app_dev.yaml\n')
            tmp.write(
                '  FIREBASE_AUTH_EMULATOR_HOST: "%s:9099"\n' % firebase_host)
            tmp.write('version: default')

        app_yaml_temp_file = tempfile.NamedTemporaryFile()
        # Here MyPy assumes that the 'name' attribute is read-only. In order to
        # silence the MyPy complaints `setattr` is used to set the attribute.
        setattr(app_yaml_temp_file, 'name', mock_yaml_filepath)
        with utils.open_file(mock_yaml_filepath, 'w') as tmp:
            tmp.write('Initial content in mock_app.yaml')

        with app_dev_yaml_filepath_swap, app_yaml_filepath_swap:
            with env_vars_to_remove_from_deployed_app_yaml_swap:
                with self.assertRaisesRegex(
                        Exception,
                        'Environment variable \'DATASTORE_HOST\' to be '
                        'removed does not exist.'
                ):
                    build.generate_app_yaml(deploy_mode=True)

        with utils.open_file(mock_yaml_filepath, 'r') as yaml_file:
            content = yaml_file.read()

        self.assertEqual(content, 'Initial content in mock_app.yaml')

        app_yaml_temp_file.close()
        app_dev_yaml_temp_file.close()

    def test_safe_delete_file(self) -> None:
        """Test safe_delete_file with both existent and non-existent
        filepath.
        """
        temp_file = tempfile.NamedTemporaryFile()
        # Here MyPy assumes that the 'name' attribute is read-only. In order to
        # silence the MyPy complaints `setattr` is used to set the attribute.
        setattr(temp_file, 'name', 'some_file.txt')
        with utils.open_file('some_file.txt', 'w') as tmp:
            tmp.write(u'Some content.')
        self.assertTrue(os.path.isfile('some_file.txt'))

        build.safe_delete_file('some_file.txt')
        self.assertFalse(os.path.isfile('some_file.txt'))

        non_existent_filepaths = [INVALID_INPUT_FILEPATH]
        # Escape the special characters, like '\', in the file paths.
        # The '\' character is usually seem in Windows style path.
        # https://docs.python.org/2/library/os.html#os.sep
        # https://docs.python.org/2/library/re.html#regular-expression-syntax
        error_message = ('File %s does not exist.') % re.escape(
            non_existent_filepaths[0])
        # Exception will be raised at first file determined to be non-existent.
        with self.assertRaisesRegex(
            OSError, error_message):
            build.safe_delete_file(non_existent_filepaths[0])

    def test_minify_third_party_libs(self) -> None:

        def _mock_safe_delete_file(unused_filepath: str) -> None:
            """Mocks build.safe_delete_file()."""
            pass

        self.assertFalse(os.path.isfile(
            'core/tests/data/third_party/css/third_party.min.css'))
        self.assertFalse(os.path.isfile(
            'core/tests/data/third_party/js/third_party.min.js'))
        self.assertFalse(os.path.isfile(
            'core/tests/data/third_party/js/third_party.min.js.map'))

        with self.swap(build, 'safe_delete_file', _mock_safe_delete_file):
            build.minify_third_party_libs('core/tests/data/third_party')

        self.assertTrue(os.path.isfile(
            'core/tests/data/third_party/css/third_party.min.css'))
        self.assertTrue(os.path.isfile(
            'core/tests/data/third_party/js/third_party.min.js'))
        self.assertTrue(os.path.isfile(
            'core/tests/data/third_party/js/third_party.min.js.map'))

        self.assertLess(
            os.path.getsize(
                'core/tests/data/third_party/css/third_party.min.css'),
            os.path.getsize('core/tests/data/third_party/css/third_party.css'))
        self.assertLess(
            os.path.getsize(
                'core/tests/data/third_party/js/third_party.min.js'),
            os.path.getsize('core/tests/data/third_party/js/third_party.js'))

        build.safe_delete_file(
            'core/tests/data/third_party/css/third_party.min.css')
        build.safe_delete_file(
            'core/tests/data/third_party/js/third_party.min.js')
        build.safe_delete_file(
            'core/tests/data/third_party/js/third_party.min.js.map')

    def test_clean(self) -> None:
        check_function_calls = {
            'safe_delete_directory_tree_gets_called': 0,
        }
        expected_check_function_calls = {
            'safe_delete_directory_tree_gets_called': 3,
        }

        def mock_safe_delete_directory_tree(unused_path: str) -> None:
            check_function_calls['safe_delete_directory_tree_gets_called'] += 1

        with self.swap(
            build, 'safe_delete_directory_tree',
            mock_safe_delete_directory_tree
        ):
            build.clean()
        self.assertEqual(check_function_calls, expected_check_function_calls)

    def test_build_with_prod_env(self) -> None:
        check_function_calls = {
            'build_using_webpack_gets_called': False,
            'ensure_files_exist_gets_called': False,
            'modify_constants_gets_called': False,
            'compare_file_count_gets_called': False,
            'generate_python_package_called': False,
            'clean_gets_called': False,
        }
        expected_check_function_calls = {
            'build_using_webpack_gets_called': True,
            'ensure_files_exist_gets_called': True,
            'modify_constants_gets_called': True,
            'compare_file_count_gets_called': True,
            'generate_python_package_called': True,
            'clean_gets_called': True,
        }

        expected_config_path = build.WEBPACK_PROD_CONFIG

        def mock_build_using_webpack(config_path: str) -> None:
            self.assertEqual(config_path, expected_config_path)
            check_function_calls['build_using_webpack_gets_called'] = True

        def mock_ensure_files_exist(unused_filepaths: List[str]) -> None:
            check_function_calls['ensure_files_exist_gets_called'] = True

        def mock_modify_constants(
            prod_env: bool,  # pylint: disable=unused-argument
            emulator_mode: bool,  # pylint: disable=unused-argument
            maintenance_mode: bool  # pylint: disable=unused-argument
        ) -> None:  # pylint: disable=unused-argument
            check_function_calls['modify_constants_gets_called'] = True

        def mock_compare_file_count(
            unused_first_dir: str,
            unused_second_dir: str
        ) -> None:
            check_function_calls['compare_file_count_gets_called'] = True

        def mock_generate_python_package() -> None:
            check_function_calls['generate_python_package_called'] = True

        def mock_clean() -> None:
            check_function_calls['clean_gets_called'] = True

        ensure_files_exist_swap = self.swap(
            build, '_ensure_files_exist', mock_ensure_files_exist)
        build_using_webpack_swap = self.swap(
            build, 'build_using_webpack', mock_build_using_webpack)
        modify_constants_swap = self.swap(
            common, 'modify_constants', mock_modify_constants)
        compare_file_count_swap = self.swap(
            build, '_compare_file_count', mock_compare_file_count)
        generate_python_package_swap = self.swap(
            build, 'generate_python_package', mock_generate_python_package)
        clean_swap = self.swap(build, 'clean', mock_clean)

        with ensure_files_exist_swap, build_using_webpack_swap, clean_swap:
            with modify_constants_swap, compare_file_count_swap:
                with generate_python_package_swap:
                    build.main(args=['--prod_env'])

        self.assertEqual(check_function_calls, expected_check_function_calls)

    def test_build_with_prod_source_maps(self) -> None:
        check_function_calls = {
            'build_using_webpack_gets_called': False,
            'ensure_files_exist_gets_called': False,
            'modify_constants_gets_called': False,
            'compare_file_count_gets_called': False,
            'clean_gets_called': False,
        }
        expected_check_function_calls = {
            'build_using_webpack_gets_called': True,
            'ensure_files_exist_gets_called': True,
            'modify_constants_gets_called': True,
            'compare_file_count_gets_called': True,
            'clean_gets_called': True,
        }

        expected_config_path = build.WEBPACK_PROD_SOURCE_MAPS_CONFIG

        def mock_build_using_webpack(config_path: str) -> None:
            self.assertEqual(config_path, expected_config_path)
            check_function_calls['build_using_webpack_gets_called'] = True

        def mock_ensure_files_exist(unused_filepaths: List[str]) -> None:
            check_function_calls['ensure_files_exist_gets_called'] = True

        def mock_modify_constants(
            prod_env: bool,  # pylint: disable=unused-argument
            emulator_mode: bool,  # pylint: disable=unused-argument
            maintenance_mode: bool  # pylint: disable=unused-argument
        ) -> None:
            check_function_calls['modify_constants_gets_called'] = True

        def mock_compare_file_count(
            unused_first_dir: str, unused_second_dir: str
        ) -> None:
            check_function_calls['compare_file_count_gets_called'] = True

        def mock_clean() -> None:
            check_function_calls['clean_gets_called'] = True

        ensure_files_exist_swap = self.swap(
            build, '_ensure_files_exist', mock_ensure_files_exist)
        build_using_webpack_swap = self.swap(
            build, 'build_using_webpack', mock_build_using_webpack)
        modify_constants_swap = self.swap(
            common, 'modify_constants', mock_modify_constants)
        compare_file_count_swap = self.swap(
            build, '_compare_file_count', mock_compare_file_count)
        clean_swap = self.swap(build, 'clean', mock_clean)
        install_python_dev_dependencies_swap = self.swap_with_checks(
            install_python_dev_dependencies,
            'main',
            lambda _: None,
            expected_args=[(['--uninstall'],)]
        )

        with ensure_files_exist_swap, build_using_webpack_swap:
            with modify_constants_swap, compare_file_count_swap:
                with clean_swap, install_python_dev_dependencies_swap:
                    build.main(args=['--prod_env', '--source_maps'])

        self.assertEqual(check_function_calls, expected_check_function_calls)

    def test_build_with_watcher(self) -> None:
        check_function_calls = {
            'ensure_files_exist_gets_called': False,
            'modify_constants_gets_called': False,
            'clean_gets_called': False,
        }
        expected_check_function_calls = {
            'ensure_files_exist_gets_called': True,
            'modify_constants_gets_called': True,
            'clean_gets_called': True,
        }

        def mock_ensure_files_exist(unused_filepaths: List[str]) -> None:
            check_function_calls['ensure_files_exist_gets_called'] = True

        def mock_modify_constants(
            prod_env: bool,  # pylint: disable=unused-argument
            emulator_mode: bool,  # pylint: disable=unused-argument
            maintenance_mode: bool   # pylint: disable=unused-argument
        ) -> None:
            check_function_calls['modify_constants_gets_called'] = True

        def mock_clean() -> None:
            check_function_calls['clean_gets_called'] = True

        ensure_files_exist_swap = self.swap(
            build, '_ensure_files_exist', mock_ensure_files_exist)
        modify_constants_swap = self.swap(
            common, 'modify_constants', mock_modify_constants)
        clean_swap = self.swap(build, 'clean', mock_clean)

        with ensure_files_exist_swap, modify_constants_swap, clean_swap:
            build.main(args=[])

        self.assertEqual(check_function_calls, expected_check_function_calls)

    def test_cannot_maintenance_mode_in_dev_mode(self) -> None:
        assert_raises_regexp_context_manager = self.assertRaisesRegex(
            Exception,
            'maintenance_mode should only be enabled in prod build.')
        with assert_raises_regexp_context_manager:
            build.main(args=['--maintenance_mode'])

    def test_cannot_minify_third_party_libs_in_dev_mode(self) -> None:
        check_function_calls = {
            'ensure_files_exist_gets_called': False,
            'clean_gets_called': False,
        }
        expected_check_function_calls = {
            'ensure_files_exist_gets_called': True,
            'clean_gets_called': True,
        }

        def mock_ensure_files_exist(unused_filepaths: List[str]) -> None:
            check_function_calls['ensure_files_exist_gets_called'] = True

        def mock_clean() -> None:
            check_function_calls['clean_gets_called'] = True

        ensure_files_exist_swap = self.swap(
            build, '_ensure_files_exist', mock_ensure_files_exist)
        clean_swap = self.swap(build, 'clean', mock_clean)
        assert_raises_regexp_context_manager = self.assertRaisesRegex(
            Exception,
            'minify_third_party_libs_only should not be set in non-prod env.')
        with ensure_files_exist_swap, assert_raises_regexp_context_manager:
            with clean_swap:
                build.main(args=['--minify_third_party_libs_only'])

        self.assertEqual(check_function_calls, expected_check_function_calls)

    def test_only_minify_third_party_libs_in_dev_mode(self) -> None:
        check_function_calls = {
            'ensure_files_exist_gets_called': False,
            'ensure_modify_constants_gets_called': False,
            'clean_gets_called': False,
        }
        expected_check_function_calls = {
            'ensure_files_exist_gets_called': True,
            'ensure_modify_constants_gets_called': False,
            'clean_gets_called': True,
        }

        def mock_ensure_files_exist(unused_filepaths: List[str]) -> None:
            check_function_calls['ensure_files_exist_gets_called'] = True

        def mock_modify_constants(
            unused_prod_env: bool,
            maintenance_mode: bool   # pylint: disable=unused-argument
        ) -> None:  # pylint: disable=unused-argument
            check_function_calls['ensure_modify_constants_gets_called'] = True

        def mock_clean() -> None:
            check_function_calls['clean_gets_called'] = True

        ensure_files_exist_swap = self.swap(
            build, '_ensure_files_exist', mock_ensure_files_exist)
        modify_constants_swap = self.swap(
            common, 'modify_constants', mock_modify_constants)
        clean_swap = self.swap(build, 'clean', mock_clean)
        with ensure_files_exist_swap, modify_constants_swap, clean_swap:
            build.main(args=['--prod_env', '--minify_third_party_libs_only'])

        self.assertEqual(check_function_calls, expected_check_function_calls)

    def test_build_using_webpack_command(self) -> None:

        @contextlib.contextmanager
        def mock_managed_webpack_compiler(
            config_path: str,
            max_old_space_size: int
        ) -> Iterator[scripts_test_utils.PopenStub]:
            self.assertEqual(config_path, build.WEBPACK_PROD_CONFIG)
            self.assertEqual(max_old_space_size, 8192)
            yield scripts_test_utils.PopenStub()

        def mock_get_file_count(unused_path: str) -> int:
            return 1

        webpack_compiler_swap = self.swap(
            servers, 'managed_webpack_compiler',
            mock_managed_webpack_compiler)
        get_file_count_swap = self.swap(
            build, 'get_file_count', mock_get_file_count)

        with webpack_compiler_swap, get_file_count_swap:
            build.build_using_webpack(build.WEBPACK_PROD_CONFIG)

    def test_build_using_webpack_command_with_incorrect_filecount_fails(
        self
    ) -> None:

        @contextlib.contextmanager
        def mock_managed_webpack_compiler(
            config_path: str, max_old_space_size: int
        ) -> Iterator[scripts_test_utils.PopenStub]:
            self.assertEqual(config_path, build.WEBPACK_PROD_CONFIG)
            self.assertEqual(max_old_space_size, 8192)
            yield scripts_test_utils.PopenStub()

        def mock_get_file_count(unused_path: str) -> int:
            return 0

        webpack_compiler_swap = self.swap(
            servers, 'managed_webpack_compiler',
            mock_managed_webpack_compiler)
        get_file_count_swap = self.swap(
            build, 'get_file_count', mock_get_file_count)

        with webpack_compiler_swap, get_file_count_swap:
            with self.assertRaisesRegex(
                AssertionError, 'webpack_bundles should be non-empty.'
            ):
                build.build_using_webpack(build.WEBPACK_PROD_CONFIG)


class E2EAndAcceptanceBuildTests(test_utils.GenericTestBase):
    """Test the end to end build methods."""

    def setUp(self) -> None:
        super().setUp()
        self.exit_stack = contextlib.ExitStack()

    def tearDown(self) -> None:
        try:
            self.exit_stack.close()
        finally:
            super().tearDown()

    def test_run_webpack_compilation_success(self) -> None:
        old_os_path_isdir = os.path.isdir

        def mock_os_path_isdir(path: str) -> bool:
            if path == 'webpack_bundles':
                return True
            return old_os_path_isdir(path)

        # The webpack compilation processes will be called 4 times as mock_isdir
        # will return true after 4 calls.
        self.exit_stack.enter_context(self.swap_with_checks(
            servers, 'managed_webpack_compiler', mock_managed_process))
        self.exit_stack.enter_context(self.swap_with_checks(
            sys, 'exit', lambda _: None, called=False))
        self.exit_stack.enter_context(self.swap_with_checks(
            os.path, 'isdir', mock_os_path_isdir))

        build.run_webpack_compilation()

    def test_run_webpack_compilation_failed(self) -> None:
        old_os_path_isdir = os.path.isdir

        def mock_os_path_isdir(path: str) -> bool:
            if path == 'webpack_bundles':
                return False
            return old_os_path_isdir(path)

        # The webpack compilation processes will be called five times.
        self.exit_stack.enter_context(self.swap_with_checks(
            servers, 'managed_webpack_compiler', mock_managed_process))
        self.exit_stack.enter_context(self.swap_with_checks(
            os.path, 'isdir', mock_os_path_isdir))
        self.exit_stack.enter_context(self.swap_with_checks(
            sys, 'exit', lambda _: None, expected_args=[(1,)]))

        build.run_webpack_compilation()

    def test_build_js_files_in_dev_mode_with_hash_file_exists(self) -> None:
        old_os_path_isdir = os.path.isdir

        def mock_os_path_isdir(path: str) -> bool:
            if path == 'webpack_bundles':
                return True
            return old_os_path_isdir(path)

        self.exit_stack.enter_context(self.swap_with_checks(
            servers, 'managed_webpack_compiler', mock_managed_process))
        self.exit_stack.enter_context(self.swap_with_checks(
            build, 'main', lambda *_, **__: None,
            expected_kwargs=[{'args': []}]))
        self.exit_stack.enter_context(self.swap_with_checks(
            os.path, 'isdir', mock_os_path_isdir))
        self.exit_stack.enter_context(self.swap_with_checks(
            sys, 'exit', lambda _: None, called=False))

        build.build_js_files(True)

    def test_build_js_files_in_dev_mode_with_exception_raised(self) -> None:
        return_code = 2
        self.exit_stack.enter_context(self.swap_to_always_raise(
            servers, 'managed_webpack_compiler',
            error=subprocess.CalledProcessError(return_code, [])))
        self.exit_stack.enter_context(self.swap_with_checks(
            build, 'main', lambda *_, **__: None,
            expected_kwargs=[{'args': []}]))
        self.exit_stack.enter_context(self.swap_with_checks(
            sys, 'exit', lambda _: None,
            expected_args=[
                # When the code under test runs, the first sys.exit call halts
                # execution. However, when this test runs, sys.exit is mocked
                # and so does not interrupt the execution flow. Therefore we
                # call sys.exit with the error code from the webpack compilation
                # process (2) 5 times (the maximum number of attempts allowed to
                # compile webpack) and then exit with code 1 after giving up
                # trying to compile webpack.
                (return_code,),
                (return_code,),
                (return_code,),
                (return_code,),
                (return_code,),
                (1,),
            ]))

        build.build_js_files(True)

    def test_build_js_files_in_prod_mode(self) -> None:
        self.exit_stack.enter_context(self.swap_with_checks(
            common, 'run_cmd', lambda *_: None, called=False))
        self.exit_stack.enter_context(self.swap_with_checks(
            build, 'main', lambda *_, **__: None,
            expected_kwargs=[{'args': ['--prod_env']}]))

        build.build_js_files(False)

    def test_build_js_files_in_prod_mode_with_source_maps(self) -> None:
        self.exit_stack.enter_context(self.swap_with_checks(
            common, 'run_cmd', lambda *_: None, called=False))
        self.exit_stack.enter_context(self.swap_with_checks(
            build, 'main', lambda *_, **__: None,
            expected_kwargs=[{'args': ['--prod_env', '--source_maps']}]))

        build.build_js_files(False, source_maps=True)

    def test_webpack_compilation_in_dev_mode_with_source_maps(self) -> None:
        self.exit_stack.enter_context(self.swap_with_checks(
            common, 'run_cmd', lambda *_: None, called=False))
        self.exit_stack.enter_context(self.swap_with_checks(
            build, 'main', lambda *_, **__: None,
            expected_kwargs=[{'args': []}]))
        self.exit_stack.enter_context(self.swap_with_checks(
            build, 'run_webpack_compilation', lambda **_: None,
            expected_kwargs=[{'source_maps': True}]))

        build.build_js_files(True, source_maps=True)