Unit tests with timestamps fail

[busunkim96]

def test_set_finding_state_flattened():
    client = SecurityCenterClient(credentials=credentials.AnonymousCredentials(),)

    # Mock the actual call within the gRPC stub, and fake the request.
    with mock.patch.object(
        type(client._transport.set_finding_state), "__call__"
    ) as call:
        # Designate an appropriate return value for the call.
        call.return_value = finding.Finding()

        # Call the method with a truthy value for each flattened field,
        # using the keyword arguments to the method.
        client.set_finding_state(
            name="name_value",
            state=finding.Finding.State.ACTIVE,
            start_time=timestamp.Timestamp(seconds=751),
        )

        # Establish that the underlying call was made with the expected
        # request object values.
        assert len(call.mock_calls) == 1
        _, args, _ = call.mock_calls[0]
        assert args[0].name == "name_value"
        assert args[0].state == finding.Finding.State.ACTIVE
        assert args[0].start_time == timestamp.Timestamp(seconds=751)

args[0].start_time is a Python datetime object and the assert fails.