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Testing Gem Command Correction Logic in TheFuck

This test suite validates the gem_unknown_command rule functionality in TheFuck project, focusing on handling incorrect Ruby gem commands and providing appropriate corrections. The tests ensure proper command matching and suggestions when users mistype gem commands.

Test Coverage Overview

The test suite provides comprehensive coverage of gem command error handling and correction scenarios. Key areas tested include:

Command matching for misspelled gem commands
Validation of correct command suggestions
Edge cases with various gem command variations
Integration with Ruby gem command output parsing

Implementation Analysis

The testing approach utilizes pytest’s parametrize feature for efficient test case management. The implementation follows fixture-based testing patterns with mocked subprocess calls to simulate gem command responses. Technical aspects include:

Parametrized test cases for different command scenarios
Mocked gem help command responses
BytesIO handling for command output simulation

Technical Details

Testing infrastructure includes:

pytest framework for test execution
mocker fixture for dependency isolation
BytesIO for stdout simulation
Command type handling from thefuck.types
Pytest parametrize for test case management

Best Practices Demonstrated

The test suite exemplifies several testing best practices in Python:

Proper test isolation using fixtures
Comprehensive positive and negative test cases
Clear test case organization using parametrize
Effective mocking of external dependencies
Maintainable test structure with clear assertions

nvbn/thefuck

tests/rules/test_gem_unknown_command.py

            
import pytest
from six import BytesIO
from thefuck.rules.gem_unknown_command import match, get_new_command
from thefuck.types import Command

output = '''
ERROR:  While executing gem ... (Gem::CommandLineError)
    Unknown command {}
'''

gem_help_commands_stdout = b'''
GEM commands are:

    build             Build a gem from a gemspec
    cert              Manage RubyGems certificates and signing settings
    check             Check a gem repository for added or missing files
    cleanup           Clean up old versions of installed gems
    contents          Display the contents of the installed gems
    dependency        Show the dependencies of an installed gem
    environment       Display information about the RubyGems environment
    fetch             Download a gem and place it in the current directory
    generate_index    Generates the index files for a gem server directory
    help              Provide help on the 'gem' command
    install           Install a gem into the local repository
    list              Display local gems whose name matches REGEXP
    lock              Generate a lockdown list of gems
    mirror            Mirror all gem files (requires rubygems-mirror)
    open              Open gem sources in editor
    outdated          Display all gems that need updates
    owner             Manage gem owners of a gem on the push server
    pristine          Restores installed gems to pristine condition from files
                      located in the gem cache
    push              Push a gem up to the gem server
    query             Query gem information in local or remote repositories
    rdoc              Generates RDoc for pre-installed gems
    search            Display remote gems whose name matches REGEXP
    server            Documentation and gem repository HTTP server
    sources           Manage the sources and cache file RubyGems uses to search
                      for gems
    specification     Display gem specification (in yaml)
    stale             List gems along with access times
    uninstall         Uninstall gems from the local repository
    unpack            Unpack an installed gem to the current directory
    update            Update installed gems to the latest version
    which             Find the location of a library file you can require
    yank              Remove a pushed gem from the index

For help on a particular command, use 'gem help COMMAND'.

Commands may be abbreviated, so long as they are unambiguous.
e.g. 'gem i rake' is short for 'gem install rake'.

'''


@pytest.fixture(autouse=True)
def gem_help_commands(mocker):
    patch = mocker.patch('subprocess.Popen')
    patch.return_value.stdout = BytesIO(gem_help_commands_stdout)
    return patch


@pytest.mark.parametrize('script, command', [
    ('gem isntall jekyll', 'isntall'),
    ('gem last --local', 'last')])
def test_match(script, command):
    assert match(Command(script, output.format(command)))


@pytest.mark.parametrize('script, output', [
    ('gem install jekyll', ''),
    ('git log', output.format('log'))])
def test_not_match(script, output):
    assert not match(Command(script, output))


@pytest.mark.parametrize('script, output, result', [
    ('gem isntall jekyll', output.format('isntall'), 'gem install jekyll'),
    ('gem last --local', output.format('last'), 'gem list --local')])
def test_get_new_command(script, output, result):
    new_command = get_new_command(Command(script, output))
    assert new_command[0] == result