def discover(self, start_dir, pattern='test*.py', top_level_dir=None):
        """Find and return all test modules from the specified start
        directory, recursing into subdirectories to find them and return all
        tests found within them. Only test files that match the pattern will
        be loaded. (Using shell style pattern matching.)

        All test modules must be importable from the top level of the project.
        If the start directory is not the top level directory then the top
        level directory must be specified separately.

        If a test package name (directory with '__init__.py') matches the
        pattern then the package will be checked for a 'load_tests' function. If
        this exists then it will be called with loader, tests, pattern.

        If load_tests exists then discovery does  *not* recurse into the package,
        load_tests is responsible for loading all tests in the package.

        The pattern is deliberately not stored as a loader attribute so that
        packages can continue discovery themselves. top_level_dir is stored so
        load_tests does not need to pass this argument in to loader.discover().
        """
        set_implicit_top = False
        if top_level_dir is None and self._top_level_dir is not None:
            # make top_level_dir optional if called from load_tests in a package
            top_level_dir = self._top_level_dir
        elif top_level_dir is None:
            set_implicit_top = True
            top_level_dir = start_dir

        top_level_dir = os.path.abspath(top_level_dir)

        if not top_level_dir in sys.path:
            # all test modules must be importable from the top level directory
            # should we *unconditionally* put the start directory in first
            # in sys.path to minimise likelihood of conflicts between installed
            # modules and development versions?
            sys.path.insert(0, top_level_dir)
        self._top_level_dir = top_level_dir

        is_not_importable = False
        if os.path.isdir(os.path.abspath(start_dir)):
            start_dir = os.path.abspath(start_dir)
            if start_dir != top_level_dir:
                is_not_importable = not os.path.isfile(os.path.join(start_dir, '__init__.py'))
        else:
            # support for discovery from dotted module names
            try:
                __import__(start_dir)
            except ImportError:
                is_not_importable = True
            else:
                the_module = sys.modules[start_dir]
                top_part = start_dir.split('.')[0]
                start_dir = os.path.abspath(os.path.dirname((the_module.__file__)))
                if set_implicit_top:
                    self._top_level_dir = self._get_directory_containing_module(top_part)
                    sys.path.remove(top_level_dir)

        if is_not_importable:
            raise ImportError('Start directory is not importable: %r' % start_dir)

        tests = list(self._find_tests(start_dir, pattern))
        return self.suiteClass(tests)
dataset/ETHPy150Open amrdraz/kodr/app/brython/www/src/Lib/unittest/loader.py/TestLoader.discover/original