Optimize checks of test database state by moving into Python.

Previously, the generate-fixtures shell script by called into Django
multiple times in order to check whether the database was in a
reasonable state.  Since there's a lot of overhead to starting up
Django, this resulted in `test-backend` and `test-js-with-casper`
being quite slow to run a single small test (2.8s or so) even on my
very fast laptop.

We fix this is by moving the checks into a new Python library, so that
we can avoid paying the Django startup overhead 3 times unnecessarily.
The result saves about 1.2s (~40%) from the time required to run a
single backend test.

Fixes #1221.

frontend_tests/run-casper

@@ -11,6 +11,7 @@ try:
     # outside a Zulip virtualenv.
     from typing import Iterable
     import requests
+    import django
 except ImportError as e:
     print("ImportError: {}".format(e))
     print("You need to run the Zulip tests inside a Zulip dev environment.")
@@ -39,6 +40,13 @@ parser.add_option('--remote-debug',
                   default=False)
 (options, args) = parser.parse_args()
 
+TOOLS_DIR = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, os.path.dirname(TOOLS_DIR))
+from zerver.lib.test_fixtures import is_template_database_current
+os.environ['DJANGO_SETTINGS_MODULE'] = 'zproject.test_settings'
+django.setup()
+os.environ['PYTHONUNBUFFERED'] = 'y'
+
 os.chdir(os.path.join(os.path.dirname(os.path.realpath(__file__)), '..'))
 
 subprocess.check_call('tools/setup/generate-test-credentials')
@@ -72,7 +80,11 @@ def run_tests(realms_have_subdomains, files):
             file = os.path.join(os.path.dirname(__file__), '../frontend_tests/casper_tests', file)
         test_files.append(os.path.abspath(file))
 
-    subprocess.check_call('tools/setup/generate-fixtures')
+    generate_fixtures_command = ['tools/setup/generate-fixtures']
+    if not is_template_database_current():
+        generate_fixtures_command.append('--force')
+
+    subprocess.check_call(generate_fixtures_command)
 
     remote_debug = ""
     if options.remote_debug:

tools/setup/generate-fixtures

@@ -2,24 +2,17 @@
 set -e
 
 function migration_status {
-    ./manage.py migrate --list --settings=zproject.test_settings | sed 's/*/ /' > "$1"
+    ./manage.py get_migration_status --settings=zproject.test_settings > $1
 }
 
-template_grep_error_code=$(echo "SELECT 1 from pg_database WHERE datname='zulip_test_template';" | python manage.py dbshell --settings=zproject.test_settings | grep -q "1 row"; echo $?)
-
-if [ "$template_grep_error_code" == "0" ]; then
-    migration_status var/available-migrations
-    if [ -e var/migration-status ] &&
-        cmp -s var/available-migrations var/migration-status &&
-        [ "$1" != "--force" ]; then
-        "$(dirname "$0")/../../scripts/setup/terminate-psql-sessions" zulip zulip_test zulip_test_base zulip_test_template
-        psql -h localhost postgres zulip_test << EOF
+if  [ "$1" != "--force" ]; then
+    "$(dirname "$0")/../../scripts/setup/terminate-psql-sessions" zulip zulip_test zulip_test_base zulip_test_template
+    psql -h localhost postgres zulip_test << EOF
 DROP DATABASE IF EXISTS zulip_test;
 CREATE DATABASE zulip_test TEMPLATE zulip_test_template;
 EOF
-        sh "$(dirname "$0")/../../scripts/setup/flush-memcached"
-        exit 0
-    fi
+    sh "$(dirname "$0")/../../scripts/setup/flush-memcached"
+    exit 0
 fi
 
 mkdir -p zerver/fixtures

tools/test-backend

@@ -23,6 +23,7 @@ if __name__ == "__main__":
     TOOLS_DIR = os.path.dirname(os.path.abspath(__file__))
     os.chdir(os.path.dirname(TOOLS_DIR))
     sys.path.insert(0, os.path.dirname(TOOLS_DIR))
+    from zerver.lib.test_fixtures import is_template_database_current
     os.environ['DJANGO_SETTINGS_MODULE'] = 'zproject.test_settings'
     # "-u" uses unbuffered IO, which is important when wrapping it in subprocess
     os.environ['PYTHONUNBUFFERED'] = 'y'
@@ -136,7 +137,11 @@ if __name__ == "__main__":
     django.setup()
 
     if options.generate_fixtures:
-        subprocess.call(os.path.join(TOOLS_DIR, 'setup', 'generate-fixtures'))
+        generate_fixtures_command = [os.path.join(TOOLS_DIR, 'setup', 'generate-fixtures')]
+        if not is_template_database_current():
+            generate_fixtures_command.append('--force')
+
+        subprocess.call(generate_fixtures_command)
 
     TestRunner = get_runner(settings)
     test_runner = TestRunner()

zerver/lib/test_fixtures.py

@@ -0,0 +1,69 @@
+# -*- coding: utf-8 -*-
+import os
+import re
+from typing import Any, Optional
+from importlib import import_module
+from six import text_type
+from six.moves import cStringIO as StringIO
+
+from django.db import connections, DEFAULT_DB_ALIAS
+from django.apps import apps
+from django.core.management import call_command
+from django.utils.module_loading import module_has_submodule
+
+def database_exists(database_name, **options):
+    # type: (text_type, **Any) -> bool
+    db = options.get('database', DEFAULT_DB_ALIAS)
+    connection = connections[db]
+
+    with connection.cursor() as cursor:
+        cursor.execute("SELECT 1 from pg_database WHERE datname='{}';".format(database_name))
+        return_value = bool(cursor.fetchone())
+    connections.close_all()
+    return return_value
+
+def get_migration_status(**options):
+    # type: (**Any) -> str
+    verbosity = options.get('verbosity', 1)
+
+    for app_config in apps.get_app_configs():
+        if module_has_submodule(app_config.module, "management"):
+            import_module('.management', app_config.name)
+
+    app_labels = [options['app_label']] if options.get('app_label') else None
+    db = options.get('database', DEFAULT_DB_ALIAS)
+    out = StringIO()
+    call_command(
+        'showmigrations',
+        '--list',
+        app_labels=app_labels,
+        database=db,
+        no_color=options.get('no_color', False),
+        settings=options.get('settings', os.environ['DJANGO_SETTINGS_MODULE']),
+        stdout=out,
+        traceback=options.get('traceback', True),
+        verbosity=verbosity,
+    )
+    connections.close_all()
+    out.seek(0)
+    output = out.read()
+    return re.sub('\x1b\[(1|0)m', '', output)
+
+def are_migrations_the_same(migration_file, **options):
+    # type: (text_type, **Any) -> bool
+    if not os.path.exists(migration_file):
+        return False
+
+    with open(migration_file) as f:
+        migration_content = f.read()
+    return migration_content == get_migration_status(**options)
+
+def is_template_database_current(
+        database_name='zulip_test_template',
+        migration_status='var/migration-status',
+        settings='zproject.test_settings'
+    ):
+    # type: (Optional[text_type], Optional[text_type], Optional[text_type]) -> bool
+    if database_exists(database_name):
+        return are_migrations_the_same(migration_status, settings=settings)
+    return False

zerver/management/commands/get_migration_status.py

@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+import argparse
+from typing import Any
+from django.db import DEFAULT_DB_ALIAS
+from django.core.management.base import BaseCommand
+
+from zerver.lib.test_fixtures import get_migration_status
+
+
+class Command(BaseCommand):
+    help = "Get status of migrations."
+
+    def add_arguments(self, parser):
+        # type: (argparse.ArgumentParser) -> None
+        parser.add_argument('app_label', nargs='?',
+            help='App label of an application to synchronize the state.')
+
+        parser.add_argument('--database', action='store', dest='database',
+            default=DEFAULT_DB_ALIAS, help='Nominates a database to synchronize. '
+                'Defaults to the "default" database.')
+
+    def handle(self, *args, **options):
+        # type: (*Any, **Any) -> None
+        self.stdout.write(get_migration_status(**options))