[harness-automation] fix case selection issue when using Chrome 80 (#4648)

elem.txt might be null when the required reference devices could not
be met (either due to the quantity or the type) for specific test.
perform() will throw exceptions if elem.text is null since Chrome and
chromedriver 80. If elem is not shown in current case list window,
move_to_element() will not work either.

tools/harness-automation/autothreadharness/harness_case.py

@@ -882,6 +882,15 @@ class HarnessCase(unittest.TestCase):
         finder = re.compile(r'.*\b' + case + r'\b')
         finder_dotted = re.compile(r'.*\b' + case.replace(' ', r'\.') + r'\b')
         for elem in elems:
+            # elem.txt might be null when the required reference devices could
+            # not be met (either due to the quantity or the type) for specific test.
+            # perform() will throw exceptions if elem.text is null since Chrome
+            # and chromedriver 80. If elem is not shown in current case list
+            # window, move_to_element() will not work either.
+            if not elem.text:
+                continue
+            # execute a javascript to scroll the window to the elem
+            self._browser.execute_script('arguments[0].scrollIntoView();', elem)
             action_chains = ActionChains(self._browser)
             action_chains.move_to_element(elem)
             action_chains.perform()