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Testing Yarn Command Correction Handler in TheFuck

This test suite validates the yarn_command_not_found rule functionality in TheFuck project, ensuring correct handling of misspelled Yarn commands and providing appropriate command corrections.

Test Coverage Overview

The test suite covers error handling for invalid Yarn commands, focusing on command matching and correction suggestions. Key test cases include:

Command pattern matching for invalid Yarn commands
Command correction suggestions for common typos
Edge cases with similar command names
Integration with Yarn’s help output parsing

Implementation Analysis

Testing approach utilizes pytest’s parametrize feature for comprehensive command verification scenarios. The implementation employs mocking techniques to simulate Yarn’s help output and validates both matching logic and command correction accuracy.

Pattern matching focuses on command string analysis and replacement suggestions based on Yarn’s available command list.

Technical Details

Testing tools and configuration include:

pytest for test framework
BytesIO for stdout simulation
Mocking with pytest fixtures
Parametrized test cases for multiple scenarios
Command object usage for standardized input handling

Best Practices Demonstrated

The test suite demonstrates several testing best practices including:

Fixture usage for common setup requirements
Separate positive and negative test cases
Parametrized testing for multiple scenarios
Clear test case organization and naming
Proper mocking of external dependencies

nvbn/thefuck

tests/rules/test_yarn_command_not_found.py

            
# -*- encoding: utf-8 -*-

from io import BytesIO
import pytest
from thefuck.types import Command
from thefuck.rules.yarn_command_not_found import match, get_new_command

output = '''
error Command "{}" not found.
'''.format

yarn_help_stdout = b'''

  Usage: yarn [command] [flags]

  Options:

    -h, --help                      output usage information
    -V, --version                   output the version number
    --verbose                       output verbose messages on internal operations
    --offline                       trigger an error if any required dependencies are not available in local cache
    --prefer-offline                use network only if dependencies are not available in local cache
    --strict-semver                 
    --json                          
    --ignore-scripts                don't run lifecycle scripts
    --har                           save HAR output of network traffic
    --ignore-platform               ignore platform checks
    --ignore-engines                ignore engines check
    --ignore-optional               ignore optional dependencies
    --force                         ignore all caches
    --no-bin-links                  don't generate bin links when setting up packages
    --flat                          only allow one version of a package
    --prod, --production [prod]     
    --no-lockfile                   don't read or generate a lockfile
    --pure-lockfile                 don't generate a lockfile
    --frozen-lockfile               don't generate a lockfile and fail if an update is needed
    --link-duplicates               create hardlinks to the repeated modules in node_modules
    --global-folder <path>          
    --modules-folder <path>         rather than installing modules into the node_modules folder relative to the cwd, output them here
    --cache-folder <path>           specify a custom folder to store the yarn cache
    --mutex <type>[:specifier]      use a mutex to ensure only one yarn instance is executing
    --no-emoji                      disable emoji in output
    --proxy <host>                  
    --https-proxy <host>            
    --no-progress                   disable progress bar
    --network-concurrency <number>  maximum number of concurrent network requests

  Commands:

    - access
    - add
    - bin
    - cache
    - check
    - clean
    - config
    - generate-lock-entry
    - global
    - import
    - info
    - init
    - install
    - licenses
    - link
    - list
    - login
    - logout
    - outdated
    - owner
    - pack
    - publish
    - remove
    - run
    - tag
    - team
    - unlink
    - upgrade
    - upgrade-interactive
    - version
    - versions
    - why

  Run `yarn help COMMAND` for more information on specific commands.
  Visit https://yarnpkg.com/en/docs/cli/ to learn more about Yarn.
''' # noqa


@pytest.fixture(autouse=True)
def yarn_help(mocker):
    patch = mocker.patch('thefuck.rules.yarn_command_not_found.Popen')
    patch.return_value.stdout = BytesIO(yarn_help_stdout)
    return patch


@pytest.mark.parametrize('command', [
    Command('yarn whyy webpack', output('whyy'))])
def test_match(command):
    assert match(command)


@pytest.mark.parametrize('command', [
    Command('npm nuild', output('nuild')),
    Command('yarn install', '')])
def test_not_match(command):
    assert not match(command)


@pytest.mark.parametrize('command, result', [
    (Command('yarn whyy webpack', output('whyy')),
     'yarn why webpack'),
    (Command('yarn require lodash', output('require')),
     'yarn add lodash')])
def test_get_new_command(command, result):
    fixed_command = get_new_command(command)
    if isinstance(fixed_command, list):
        fixed_command = fixed_command[0]

    assert fixed_command == result