apache/beam · error · ValueError

At most one of --create_test and --fix_tests may be specifie

Error message

At most one of --create_test and --fix_tests may be specified.

What it means

run_tests supports generating a new test (--create_test) or updating existing tests (--fix_tests), but not both simultaneously, since the two modes are mutually exclusive workflows. Passing both raises this ValueError.

Source

Thrown at sdks/python/apache_beam/yaml/main.py:169

  return pipeline_yaml


def run(argv=None):
  options, constructor, display_data = build_pipeline_components_from_argv(argv)
  with beam.Pipeline(options=options, display_data=display_data) as p:
    print('Building pipeline...')
    constructor(p)
    print('Running pipeline...')


def run_tests(argv=None, exit=True):
  known_args, pipeline_args, _, pipeline_yaml = _build_pipeline_yaml_from_argv(
      argv)
  pipeline_spec = yaml.load(pipeline_yaml, Loader=yaml_transform.SafeLineLoader)
  options = _build_pipeline_options(pipeline_spec, pipeline_args)

  if known_args.create_test and known_args.fix_tests:
    raise ValueError(
        'At most one of --create_test and --fix_tests may be specified.')
  elif known_args.create_test:
    result = unittest.TestResult()
    tests = []
  else:
    if known_args.test_suite:
      with open(known_args.test_suite) as fin:
        test_suite_holder = yaml.load(
            fin, Loader=yaml_transform.SafeLineLoader) or {}
    else:
      test_suite_holder = pipeline_spec
    test_specs = test_suite_holder.get('tests', [])
    if not isinstance(test_specs, list):
      raise TypeError('tests attribute must be a list of test specifications.')
    elif not test_specs:
      raise RuntimeError(
          'No tests found. '
          "If you haven't added a set of tests yet, you can get started by "

View on GitHub (pinned to 12126d8942)

Solutions

Choose one mode: drop --fix_tests if you want to generate a fresh test, or drop --create_test to update existing tests.
In scripts, gate each flag on distinct user intent (e.g. MODE=create|fix) so both are never emitted.
Wrap the call in try/except ValueError to translate the message into a friendly CLI usage error.
Document the mutual exclusivity in your team's pipeline-testing docs/aliases.

Example fix

# before
python -m apache_beam.yaml.main --yaml_pipeline_file p.yaml --create_test --fix_tests
# after
python -m apache_beam.yaml.main --yaml_pipeline_file p.yaml --fix_tests

Defensive patterns

Strategy: validation

Validate before calling

import sys
flags = sys.argv
assert not ('--create_test' in flags and '--fix_tests' in flags), 'choose --create_test OR --fix_tests'

Type guard

def has_conflicting_test_flags(argv):
    return '--create_test' in argv and '--fix_tests' in argv

Try / catch

try:
    apache_beam.yaml.main.run(argv)
except ValueError as e:
    if 'At most one of --create_test' in str(e):
        parser.error('--create_test and --fix_tests are mutually exclusive')
    raise

Prevention

Expose a single MODE=create|fix parameter in wrapper scripts instead of raw flags.
Never append both flags in CI matrices or make targets.
Document the two test-authoring modes separately in team docs.

When it happens

Trigger: Invoking apache_beam.yaml.main with both --create_test and --fix_tests flags set (e.g. `--create_test --fix_tests`), triggering the check in run_tests.

Common situations: Alias/scripts that always append --fix_tests while a user also passes --create_test; confusion between the two test-authoring modes; CI matrices enabling both toggles.

Understand the failure class

Background: "mutually exclusive" flag errors: what "can't supply both nx and xx", "--raw is not compatible with -i" and "cannot be used with" mean, and how to fix them — this error's family across 29 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/1de06bb3aa60dc96. Report an issue: GitHub.