perf(acceptance): Reuse one Chrome per worker and reset it between tests

Each acceptance test launched and quit its own Chrome. Keep one browser per
xdist worker instead, and between tests open a fresh tab, close the old ones,
and clear cookies and all origin storage (localStorage, IndexedDB, service
workers, Cache Storage) over CDP. The HTTP cache stays warm.

If the reset fails or the browser died, it is replaced with a fresh one.
Firefox keeps the old launch-per-test behavior.

Co-Authored-By: Joshua Li <14209781+joshuarli@users.noreply.github.com>

Author: sentry-junior[bot]

src/sentry/testutils/pytest/selenium.py

@@ -17,6 +17,7 @@
 )
 from selenium.webdriver.common.action_chains import ActionChains
 from selenium.webdriver.common.by import By
+from selenium.webdriver.remote.webdriver import WebDriver
 from selenium.webdriver.support import expected_conditions
 from selenium.webdriver.support.wait import WebDriverWait
 
@@ -397,14 +398,10 @@ def start_chrome(**chrome_args):
             )
 
 
-@pytest.fixture(scope="function")
-def browser(request, live_server):
-    window_size = request.config.getoption("window_size")
-    window_width, window_height = map(int, window_size.split("x", 1))
-
-    driver_type = request.config.getoption("selenium_driver")
-    headless = not request.config.getoption("no_headless")
-    slow_network = request.config.getoption("slow_network")
+def _start_driver(config):
+    window_size = config.getoption("window_size")
+    driver_type = config.getoption("selenium_driver")
+    headless = not config.getoption("no_headless")
     if driver_type == "chrome":
         options = webdriver.ChromeOptions()
         options.add_argument("no-sandbox")
@@ -413,26 +410,85 @@ def browser(request, live_server):
         options.add_argument(f"window-size={window_size}")
         if headless:
             options.add_argument("headless")
-        chrome_path = request.config.getoption("chrome_path")
+        chrome_path = config.getoption("chrome_path")
         if chrome_path:
             options.binary_location = chrome_path
-        chromedriver_path = request.config.getoption("chromedriver_path")
+        chromedriver_path = config.getoption("chromedriver_path")
         chrome_args = {"options": options}
         if chromedriver_path:
             chrome_args["executable_path"] = chromedriver_path
 
-        driver = start_chrome(**chrome_args)
-        if slow_network:
-            driver.set_network_conditions(
-                offline=False,
-                latency=400 * 2,  # additional latency (ms)
-                throughput=500 * 1024,  # maximal throughput
-            )
+        return start_chrome(**chrome_args)
     elif driver_type == "firefox":
-        driver = webdriver.Firefox()
+        return webdriver.Firefox()
     else:
         raise pytest.UsageError("--driver must be specified")
 
+
+def _quit_driver(driver):
+    try:
+        driver.quit()
+    except Exception:
+        pass
+
+
+def _reset_chrome(driver, origin):
+    # A new tab drops sessionStorage, per-tab CDP emulation overrides, and any
+    # JS or requests the previous test's page still has in flight, which must
+    # stop before the database is flushed.
+    previous_handles = driver.window_handles
+    driver.switch_to.new_window("tab")
+    fresh_handle = driver.current_window_handle
+    for handle in previous_handles:
+        driver.switch_to.window(handle)
+        driver.close()
+    driver.switch_to.window(fresh_handle)
+
+    # The HTTP cache stays warm: the app cannot read it, and a cold cache
+    # would give back part of what skipping the relaunch saves.
+    driver.execute_cdp_cmd("Network.clearBrowserCookies", {})
+    driver.execute_cdp_cmd("Storage.clearDataForOrigin", {"origin": origin, "storageTypes": "all"})
+
+
+class _SessionDriver:
+    driver: WebDriver | None = None
+
+
+@pytest.fixture(scope="session")
+def _session_driver():
+    # Session scope is per xdist worker, so each worker owns one Chrome.
+    holder = _SessionDriver()
+    yield holder
+    if holder.driver is not None:
+        _quit_driver(holder.driver)
+
+
+@pytest.fixture(scope="function")
+def browser(request, live_server, _session_driver):
+    window_size = request.config.getoption("window_size")
+    window_width, window_height = map(int, window_size.split("x", 1))
+    reuse = request.config.getoption("selenium_driver") == "chrome"
+
+    driver = _session_driver.driver if reuse else None
+    if driver is not None:
+        try:
+            driver.window_handles
+        except WebDriverException:
+            logger.warning("selenium.reused-browser-dead", exc_info=True)
+            _quit_driver(driver)
+            driver = None
+    if driver is None:
+        driver = _start_driver(request.config)
+        if reuse:
+            _session_driver.driver = driver
+
+    if request.config.getoption("slow_network"):
+        driver.set_network_conditions(
+            offline=False,
+            latency=400 * 2,  # additional latency (ms)
+            throughput=500 * 1024,  # maximal throughput
+        )
+
     driver.set_window_size(window_width, window_height)
 
     request.node._driver = driver
@@ -462,11 +518,19 @@ def browser(request, live_server):
         sys.stderr.write("[browser console] ")
         sys.stderr.write(repr(entry))
         sys.stderr.write("\n")
-    # Teardown Selenium.
+
+    if not reuse:
+        _quit_driver(driver)
+        return
+
     try:
-        driver.quit()
+        _reset_chrome(driver, live_server.url)
     except Exception:
-        pass
+        # A browser that cannot be reset could leak state into the next test,
+        # so replace it instead.
+        logger.warning("selenium.reset-failed", exc_info=True)
+        _session_driver.driver = None
+        _quit_driver(driver)
 
 
 @pytest.hookimpl(tryfirst=True, hookwrapper=True)