Revert "chore: move retry async check to wrap time (#649)"

This reverts commit ac098a7.

Author: parthea

google/api_core/retry/retry_unary.py

@@ -141,7 +141,10 @@ def retry_target(
 
     for sleep in sleep_generator:
         try:
-            return target()
+            result = target()
+            if inspect.isawaitable(result):
+                warnings.warn(_ASYNC_RETRY_WARNING)
+            return result
 
         # pylint: disable=broad-except
         # This function explicitly must deal with broad exceptions.
@@ -277,8 +280,6 @@ def __call__(
             Callable: A callable that will invoke ``func`` with retry
                 behavior.
         """
-        if inspect.iscoroutinefunction(func):
-            warnings.warn(_ASYNC_RETRY_WARNING)
         if self._on_error is not None:
             on_error = self._on_error
 

tests/unit/retry/test_retry_unary.py

@@ -101,20 +101,14 @@ def test_retry_target_non_retryable_error(utcnow, sleep):
 )
 @pytest.mark.asyncio
 async def test_retry_target_warning_for_retry(utcnow, sleep):
-    """
-    retry.Retry should raise warning when wrapping an async function.
-    """
-
-    async def target():
-        pass  # pragma: NO COVER
-
-    retry_obj = retry.Retry()
+    predicate = retry.if_exception_type(ValueError)
+    target = mock.AsyncMock(spec=["__call__"])
 
     with pytest.warns(Warning) as exc_info:
-        # raise warning when wrapping an async function
-        retry_obj(target)
+        # Note: predicate is just a filler and doesn't affect the test
+        retry.retry_target(target, predicate, range(10), None)
 
-    assert len(exc_info) == 1
+    assert len(exc_info) == 2
     assert str(exc_info[0].message) == retry.retry_unary._ASYNC_RETRY_WARNING
     sleep.assert_not_called()