Fixed #25647 -- Reverted "Simplified deduplication of test databases."

    return groups

def get_unique_databases():

def get_unique_databases_and_mirrors():

    """

    Figure out which databases actually need to be created.

    Deduplicate entries in DATABASES that correspond the same database or are

    configured as test mirrors.

    Returns an ordered mapping of signatures to (name, list of aliases)

    where all aliases share the same unerlying database.

    Return two values:

    - test_databases: ordered mapping of signatures to (name, list of aliases)

                      where all aliases share the same underlying database.

    - mirrored_aliases: mapping of mirror aliases to original aliases.

    """

    mirrored_aliases = {}

    test_databases = {}

    dependencies = {}

    default_sig = connections[DEFAULT_DB_ALIAS].creation.test_db_signature()

        test_settings = connection.settings_dict['TEST']

        if test_settings['MIRROR']:

            target = test_settings['MIRROR']

            signature = connections[target].creation.test_db_signature()

            # If the database is marked as a test mirror, save the alias.

            mirrored_aliases[alias] = test_settings['MIRROR']

        else:

            signature = connection.creation.test_db_signature()

            if 'DEPENDENCIES' in test_settings:

                dependencies[alias] = test_settings['DEPENDENCIES']

            elif alias != DEFAULT_DB_ALIAS and signature != default_sig:

                dependencies[alias] = test_settings.get('DEPENDENCIES', [DEFAULT_DB_ALIAS])

            # Store a tuple with DB parameters that uniquely identify it.

            # If we have two aliases with the same values for that tuple,

            # we only need to create the test database once.

            item = test_databases.setdefault(

            signature, (connection.settings_dict['NAME'], set()))

                connection.creation.test_db_signature(),

                (connection.settings_dict['NAME'], set())

            )

            item[1].add(alias)

            if 'DEPENDENCIES' in test_settings:

                dependencies[alias] = test_settings['DEPENDENCIES']

            else:

                if alias != DEFAULT_DB_ALIAS and connection.creation.test_db_signature() != default_sig:

                    dependencies[alias] = test_settings.get('DEPENDENCIES', [DEFAULT_DB_ALIAS])

    test_databases = dependency_ordered(test_databases.items(), dependencies)

    test_databases = collections.OrderedDict(test_databases)

    return test_databases

    return test_databases, mirrored_aliases

def setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, **kwargs):

    """

    Creates the test databases.

    """

    test_databases = get_unique_databases()

    test_databases, mirrored_aliases = get_unique_databases_and_mirrors()

    old_names = []

                connections[alias].creation.set_as_test_mirror(

                    connections[first_alias].settings_dict)

    # Configure the test mirrors.

    for alias, mirror_alias in mirrored_aliases.items():

        connections[alias].creation.set_as_test_mirror(

            connections[mirror_alias].settings_dict)

    if debug_sql:

        for alias in connections:

            connections[alias].force_debug_cursor = True