test(meta): control JS bundle sizes (frappe#17244)

Any drastic increase in production bundle sizes should fail in CI.

frappe/tests/test_commands.py

@@ -12,6 +12,7 @@
 from contextlib import contextmanager
 from functools import wraps
 from glob import glob
+from pathlib import Path
 from typing import List, Optional
 from unittest.case import skipIf
 from unittest.mock import patch
@@ -31,6 +32,7 @@
 from frappe.tests.test_query_builder import run_only_if
 from frappe.utils import add_to_date, get_bench_path, get_bench_relative_path, now
 from frappe.utils.backups import fetch_latest_backups
+from frappe.utils.jinja_globals import bundled_asset
 
 _result: Optional[Result] = None
 TEST_SITE = "commands-site-O4PN2QKA.test"  # added random string tag to avoid collisions
@@ -692,7 +694,25 @@ def test_migrate_cli(self):
 
 
 class TestBenchBuild(BaseTestCommands):
-	def test_build_assets(self):
-		with cli(frappe.commands.utils.build) as result:
+	def test_build_assets_size_check(self):
+		with cli(frappe.commands.utils.build, "--force --production") as result:
 			self.assertEqual(result.exit_code, 0)
 			self.assertEqual(result.exception, None)
+
+		CURRENT_SIZE = 3.7  # MB
+		JS_ASSET_THRESHOLD = 0.1
+
+		hooks = frappe.get_hooks()
+		default_bundle = hooks["app_include_js"]
+
+		default_bundle_size = 0.0
+
+		for chunk in default_bundle:
+			abs_path = Path.cwd() / frappe.local.sites_path / bundled_asset(chunk)[1:]
+			default_bundle_size += abs_path.stat().st_size
+
+		self.assertLessEqual(
+			default_bundle_size / (1024 * 1024),
+			CURRENT_SIZE * (1 + JS_ASSET_THRESHOLD),
+			f"Default JS bundle size increased by {JS_ASSET_THRESHOLD:.2%} or more",
+		)