6.3 On Implicit and Explicit Waits, and Voodoo time.sleeps

textbook/chap6.md

@@ -45,4 +45,38 @@ python manage.py test lists
 Sometimes, mismatch between firefox and (Selenium + Geckodriver) may result failure in test, as firefox may auto upgrade itself at night. Upgrade Selenium + Geckodriver as follow:
 
 1. `pip install --upgrade selenium`
-2. Download new geckodriver
+2. Download new geckodriver
+
+## 6.3 On Implicit and Explicit Waits, and Voodoo time.sleeps
+
+Implicit Waits & Explicit Waits:
+* Implicit Waits: Selenium tries to wait "automatically" for you when it thinks the page is loading. But it's unstable, DON'T USE IT.
+* Explicit Waits: `time.sleep(...)` in FT. It's hard to set a fixed second (Voodoo Sleep). A while loop with try/except will be more better
+
+```python
+from selenium.common.exceptions import WebDriverException
+
+MAX_WAIT = 10 # Maximum amount of time we're prepared to wait
+[...]
+
+    def wait_for_row_in_list_table(self, row_text):
+        start_time = time.time()
+        while True:
+            try:
+                table = self.browser.find_element_by_id('id_list_table')
+                rows = table.find_elements_by_tag_name('tr')
+                self.assertIn(row_text, [row.text for row in rows])
+                return
+            except (AssertionError, WebDriverException) as e:
+                if time.time() - start_time > MAX_WAIT:
+                    raise e
+                time.sleep(0.5)
+```
+
+Replace all `check_for_row_in_list_table` with `wait_for_row_in_list_table`
+
+### "BEST PRACTICES" Applied in this Chapter
+
+* Ensuring test isolation and managing global state
+* Avoid "voodoo" sleeps (i.e. `time.sleep`)
+* Don't rely on Selenium's implicit waits