Add UT

Signed-off-by: bingwang <[email protected]>

tests/dvslib/dvs_common.py

@@ -0,0 +1,55 @@
+"""Common infrastructure for writing VS tests."""
+
+import collections
+import time
+
+
+_PollingConfig = collections.namedtuple('PollingConfig', 'polling_interval timeout strict')
+
+
+class PollingConfig(_PollingConfig):
+    """PollingConfig provides parameters that are used to control polling behavior.
+
+    Attributes:
+        polling_interval (int): How often to poll, in seconds.
+        timeout (int): The maximum amount of time to wait, in seconds.
+        strict (bool): If the strict flag is set, reaching the timeout will cause tests to fail.
+    """
+
+
+def wait_for_result(
+    polling_function,
+    polling_config,
+):
+    """Run `polling_function` periodically using the specified `polling_config`.
+
+    Args:
+        polling_function: The function being polled. The function cannot take any arguments and
+            must return a status which indicates if the function was succesful or not, as well as
+            some return value.
+        polling_config: The parameters to use to poll the polling function.
+
+    Returns:
+        If the polling function succeeds, then this method will return True and the output of the
+        polling function.
+
+        If it does not succeed within the provided timeout, it will return False and whatever the
+        output of the polling function was on the final attempt.
+    """
+    if polling_config.polling_interval == 0:
+        iterations = 1
+    else:
+        iterations = int(polling_config.timeout // polling_config.polling_interval) + 1
+
+    for _ in range(iterations):
+        status, result = polling_function()
+
+        if status:
+            return (True, result)
+
+        time.sleep(polling_config.polling_interval)
+
+    if polling_config.strict:
+        assert False, "Operation timed out after {} seconds".format(polling_config.timeout)
+
+    return (False, result)