add a test for get_pdu and initialize_from_db

Add a test for get_pdu_from_db and initialize_from_db

Description

How Has This Been Tested?

Relevant Documents (optional)

Types of changes

• Adding tests

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.

Reviewers

@roscar @danilevc @hammerd

cal_tools/cal_tools/agipdlib.py

@@ -17,7 +17,7 @@ from cal_tools.agipdutils import (
 )
 from cal_tools.enums import AgipdGainMode, BadPixels, SnowResolution
 from cal_tools.tools import get_constant_from_db_and_time
-from iCalibrationDB import Conditions
+from iCalibrationDB import Conditions, Constants
 
 from cal_tools.cython import agipdalgs as calgs
 
@@ -1272,7 +1272,8 @@ class AgipdCorrections:
         return when
 
     def initialize_from_db(self, karabo_id: str, karabo_da: str,
-                           cal_db_interface: str, creation_time: str,
+                           cal_db_interface: str,
+                           creation_time: 'datetime.datetime',
                            memory_cells: float, bias_voltage: int,
                            photon_energy: float, gain_setting: float,
                            acquisition_rate: float, module_idx: int,