fix: remove default argument now from _seconds_until_refresh (#356)

Having now as a default argument means it is set once and then never
adjusted. So in subsequent calls to _seconds_until_refresh the duration
will just continue to grow larger and larger as it evaluates agains the same now

The result of this means that duration // 2 block is always being hit and
will continue to grow. It could grow to be greater than 3600 and lead to errors.

google/cloud/alloydb/connector/refresh_utils.py

@@ -26,22 +26,19 @@
 _refresh_buffer: int = 4 * 60  # 4 minutes
 
 
-def _seconds_until_refresh(
-    expiration: datetime, now: datetime = datetime.now(timezone.utc)
-) -> int:
+def _seconds_until_refresh(expiration: datetime) -> int:
     """
     Calculates the duration to wait before starting the next refresh.
     Usually the duration will be half of the time until certificate
     expiration.
 
     Args:
         expiration (datetime.datetime): Time of certificate expiration.
-        now (datetime.datetime): Current time (UTC)
     Returns:
         int: Time in seconds to wait before performing next refresh.
     """
 
-    duration = int((expiration - now).total_seconds())
+    duration = int((expiration - datetime.now(timezone.utc)).total_seconds())
 
     # if certificate duration is less than 1 hour
     if duration < 3600:

tests/unit/test_refresh_utils.py

@@ -16,6 +16,8 @@
 from datetime import timedelta
 from datetime import timezone
 
+import pytest
+
 from google.cloud.alloydb.connector.refresh_utils import _seconds_until_refresh
 
 
@@ -24,8 +26,14 @@ def test_seconds_until_refresh_over_1_hour() -> None:
     Test _seconds_until_refresh returns proper time in seconds.
     If expiration is over 1 hour, should return duration/2.
     """
-    now = datetime.now()
-    assert _seconds_until_refresh(now + timedelta(minutes=62), now) == 31 * 60
+    # using pytest.approx since sometimes can be off by a second
+    assert (
+        pytest.approx(
+            _seconds_until_refresh(datetime.now(timezone.utc) + timedelta(minutes=62)),
+            1,
+        )
+        == 31 * 60
+    )
 
 
 def test_seconds_until_refresh_under_1_hour_over_4_mins() -> None:
@@ -34,8 +42,14 @@ def test_seconds_until_refresh_under_1_hour_over_4_mins() -> None:
     If expiration is under 1 hour and over 4 minutes,
     should return duration-refresh_buffer (refresh_buffer = 4 minutes).
     """
-    now = datetime.now(timezone.utc)
-    assert _seconds_until_refresh(now + timedelta(minutes=5), now) == 60
+    # using pytest.approx since sometimes can be off by a second
+    assert (
+        pytest.approx(
+            _seconds_until_refresh(datetime.now(timezone.utc) + timedelta(minutes=5)),
+            1,
+        )
+        == 60
+    )
 
 
 def test_seconds_until_refresh_under_4_mins() -> None: