ci(acceptance): experiment: 3 xdist workers with Chrome reuse

.github/workflows/acceptance.yml

@@ -69,7 +69,7 @@ jobs:
       TEST_GROUP_STRATEGY: roundrobin
       PYTHONHASHSEED: '0'
       XDIST_PER_WORKER_SNUBA: '1'
-      XDIST_WORKERS: '2'
+      XDIST_WORKERS: '3'
 
     steps:
       - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7

src/sentry/testutils/pytest/selenium.py

@@ -13,6 +13,7 @@
 import pytest
 from selenium import webdriver
 from selenium.common.exceptions import (
+    NoAlertPresentException,
     NoSuchElementException,
     SessionNotCreatedException,
     WebDriverException,
@@ -31,6 +32,11 @@
 logger = logging.getLogger("sentry.testutils")
 
 
+# Selenium's default of 0.5s adds up to half a second to every wait that
+# isn't already satisfied, and acceptance tests wait many times each.
+WAIT_POLL_SECONDS = 0.1
+
+
 class Browser:
     def __init__(self, driver, live_server):
         self.driver = driver
@@ -214,7 +220,7 @@ def wait_until_clickable(self, selector=None, xpath=None, timeout=10):
         Waits until ``selector`` is visible and enabled to be clicked, or until ``timeout``
         is hit, whichever happens first.
         """
-        wait = WebDriverWait(self.driver, timeout)
+        wait = WebDriverWait(self.driver, timeout, poll_frequency=WAIT_POLL_SECONDS)
         if selector:
             wait.until(expected_conditions.element_to_be_clickable((By.CSS_SELECTOR, selector)))
         elif xpath:
@@ -229,7 +235,7 @@ def wait_until(self, selector=None, xpath=None, title=None, timeout=10):
         Waits until ``selector`` is found in the browser, or until ``timeout``
         is hit, whichever happens first.
         """
-        wait = WebDriverWait(self.driver, timeout)
+        wait = WebDriverWait(self.driver, timeout, poll_frequency=WAIT_POLL_SECONDS)
         if selector:
             wait.until(expected_conditions.presence_of_element_located((By.CSS_SELECTOR, selector)))
         elif xpath:
@@ -249,7 +255,7 @@ def wait_until_not(self, selector=None, xpath=None, title=None, timeout=10):
         Waits until ``selector`` is NOT found in the browser, or until
         ``timeout`` is hit, whichever happens first.
         """
-        wait = WebDriverWait(self.driver, timeout)
+        wait = WebDriverWait(self.driver, timeout, poll_frequency=WAIT_POLL_SECONDS)
         if selector:
             wait.until_not(
                 expected_conditions.presence_of_element_located((By.CSS_SELECTOR, selector))
@@ -268,7 +274,7 @@ def wait_until_script_execution(self, script, timeout=10):
         Waits until ``script`` executes and evaluates truthy,
         or until ``timeout`` is hit, whichever happens first.
         """
-        wait = WebDriverWait(self.driver, timeout)
+        wait = WebDriverWait(self.driver, timeout, poll_frequency=WAIT_POLL_SECONDS)
         wait.until(lambda driver: driver.execute_script(script))
 
         return self
@@ -499,12 +505,43 @@ def _take_prelaunched_chrome() -> webdriver.Chrome | None:
 def pytest_sessionfinish(session: pytest.Session, exitstatus: int) -> None:
     # A worker whose tests never use the browser still has to close the
     # prelaunched Chrome.
-    driver = _take_prelaunched_chrome()
-    if driver is not None:
+    for driver in (_take_prelaunched_chrome(), _reusable_chrome.pop("driver", None)):
+        if driver is not None:
+            try:
+                driver.quit()
+            except Exception:
+                pass
+
+
+# Starting Chrome for every test costs the launch, and each test then loads the
+# app bundle into a cold cache. One Chrome per worker, reset between tests,
+# keeps the cache warm.
+_reusable_chrome: dict[str, webdriver.Chrome] = {}
+
+
+def _reset_chrome(driver: webdriver.Chrome, origin: str) -> bool:
+    """Clears what a test can leave behind. Returns False if Chrome is unusable."""
+    try:
         try:
-            driver.quit()
-        except Exception:
+            driver.switch_to.alert.dismiss()
+        except NoAlertPresentException:
             pass
+        handles = driver.window_handles
+        for handle in handles[1:]:
+            driver.switch_to.window(handle)
+            driver.close()
+        driver.switch_to.window(handles[0])
+        driver.get("about:blank")
+        driver.execute_cdp_cmd("Network.clearBrowserCookies", {})
+        driver.execute_cdp_cmd(
+            "Storage.clearDataForOrigin", {"origin": origin, "storageTypes": "all"}
+        )
+        driver.execute_cdp_cmd("Emulation.setTouchEmulationEnabled", {"enabled": False})
+        driver.execute_cdp_cmd("Emulation.clearDeviceMetricsOverride", {})
+    except Exception:
+        logger.warning("selenium.reset-chrome.failed", exc_info=True)
+        return False
+    return True
 
 
 @pytest.fixture(scope="function")
@@ -515,7 +552,8 @@ def browser(request, live_server):
     driver_type = request.config.getoption("selenium_driver")
     driver: WebDriver
     if driver_type == "chrome":
-        driver = _take_prelaunched_chrome() or _launch_chrome(request.config)
+        reused = _reusable_chrome.pop("driver", None)
+        driver = reused or _take_prelaunched_chrome() or _launch_chrome(request.config)
     elif driver_type == "firefox":
         driver = webdriver.Firefox()
     else:
@@ -550,6 +588,9 @@ def browser(request, live_server):
         sys.stderr.write("[browser console] ")
         sys.stderr.write(repr(entry))
         sys.stderr.write("\n")
+    if isinstance(driver, webdriver.Chrome) and _reset_chrome(driver, live_server.url):
+        _reusable_chrome["driver"] = driver
+        return
     # Teardown Selenium.
     try:
         driver.quit()
@@ -564,7 +605,9 @@ def pytest_runtest_makereport(item, call):
     summary: MutableSequence[str] = []
     extra = getattr(report, "extra", [])
     driver = getattr(item, "_driver", None)
-    if driver is not None:
+    # Each phase of every test used to take a screenshot and dump the page
+    # source. Only a failure needs them.
+    if driver is not None and report.failed:
         _gather_url(item, report, driver, summary, extra)
         _gather_screenshot(item, report, driver, summary, extra)
         _gather_html(item, report, driver, summary, extra)