':param include_suites: List of suite names to include. If ``None`` or
an empty list, all suites are included. When executing tests
normally, these names are specified using the ``--suite`` option.
:param warn_on_skipped: Boolean to control should a warning be emitted
if a file is skipped because it cannot be parsed or should it be
ignored silently. When executing tests normally, this value is set
with the ``--warnonskippedfiles`` option.
:param extension: Limit parsing test data to only these files. Files
are specified as an extension that is handled case-insensitively.
Same as ``--extension`` on the command line.'

def __init__(self, include_suites=None, warn_on_skipped=False, extension=None):

    self.include_suites = include_suites
    self.warn_on_skipped = warn_on_skipped
    self.extensions = self._get_extensions(extension)
    builder = StepBuilder()
    self._build_steps = builder.build_steps
    self._build_step = builder.build_step
