Index: trunk/SDToolBox/extract_data.py
===================================================================
diff -u -r112 -r116
--- trunk/SDToolBox/extract_data.py	(.../extract_data.py)	(revision 112)
+++ trunk/SDToolBox/extract_data.py	(.../extract_data.py)	(revision 116)
@@ -109,6 +109,11 @@
 
         __file_iterator: list = []
 
+        def __init__(self):
+            super().__init__()
+            # Force cleaning up iterator to avoid cached issues.
+            self.__file_iterator = []
+
         # Region Abstract methods / properties.
         @property
         @abstractmethod
@@ -277,7 +282,7 @@
                 [nn_idx[1][i] for i in unique_idx]
             return new_nn_idx, \
                 [unique_nn.tolist().index(nn.tolist())
-                 for nn in combined_array]
+                    for nn in combined_array]
 
         def __get_time_ref_group(self) -> List[str]:
             return [
Index: trunk/tests/test_extract_data.py
===================================================================
diff -u -r112 -r116
--- trunk/tests/test_extract_data.py	(.../test_extract_data.py)	(revision 112)
+++ trunk/tests/test_extract_data.py	(.../test_extract_data.py)	(revision 116)
@@ -10,11 +10,79 @@
 from SDToolBox.input_data import InputData
 from SDToolBox.extract_data import ExtractData
 import SDToolBox.output_messages as om
+import numpy as np
 
 
 class Test_get_era5:
 
     @pytest.mark.systemtest
+    def test_extract_non_gridded_then_gridded(self):
+        self.test_extract_nongridded_data()
+        self.test_extract_gridded_data()
+
+    @pytest.mark.systemtest
+    def test_extract_nongridded_data(self):
+        acceptance_folder = TestUtils.get_local_test_data_dir('acceptance_tests\\data')
+        DS = Dataset(os.path.join(acceptance_folder, 'NS_WAM_ERA5.nc'))
+        assert DS
+        lonWAM = DS.variables['lon'][:]
+        latWAM = DS.variables['lat'][:]
+
+        coordsWAM = {'LON': [], 'LAT': []}
+        for i, j in zip(lonWAM, latWAM):
+            coordsWAM['LON'].append(i)
+            coordsWAM['LAT'].append(j)
+
+        # set other data variables    
+        variables = [] # saved names of the entries
+        for i in DS.variables:
+            print(i, DS.variables[i].shape)
+            variables.append(i)
+        varWAM = [v.lower() for v in variables[5:]]
+        timeWAMy = [1981] # 1987 to 2018
+
+        # use the SDToolBox function to create input data
+        Input_DataWAM = InputData(
+            input_coordinates=coordsWAM,
+            input_variables=varWAM,
+            input_scenarios=['era5'],
+            input_years=timeWAMy) # default is_gridded is false, referring to points
+
+        # use the SDToolBox function to extract data
+        # dir_test_data = 'P:\\metocean-data\\open\\ERA5\\data\\Global'
+        dir_test_data = TestUtils.get_local_test_data_dir('era5_test_data')
+        extracted_data = ExtractData.get_era_5(dir_test_data, Input_DataWAM)
+        assert extracted_data is not None
+
+
+    @pytest.mark.systemtest
+    def test_extract_gridded_data(self):
+        steplon = 0.5 # degrees
+        lonl = -5 # left lon value
+        lonr = 11 # right lon value
+        steplat = 0.5
+        latl = 50 # lower lat value
+        latu = 62 # upper lat value
+        xrang = np.arange(lonl, lonr+steplon, steplon).tolist() 
+        yrang = np.arange(latl, latu+steplat, steplat).tolist() 
+
+        coordsBOX = {'LON': xrang, 'LAT': yrang}
+        timeWAMy = [1981] # 1987 to 2018
+        # use the SDToolBox function to create input data
+        Input_DataBOX = InputData(
+            input_coordinates=coordsBOX, 
+            input_variables=['msl'], 
+            input_scenarios=['era5'],
+            input_years=timeWAMy, 
+            is_gridded = True)
+        # dir_test_data = 'P:\\metocean-data\\open\\ERA5\\data\\Global'
+        dir_test_data = TestUtils.get_local_test_data_dir('era5_test_data')
+        extracted_data = ExtractData.get_era_5(dir_test_data, Input_DataBOX)
+
+        assert extracted_data is not None
+
+
+    @pytest.mark.systemtest
     def test_given_list_of_coordinates_then_subset_is_extracted(self):
         # 1. Given
         # When using local data you can just replace the comment in these lines