Creating a test for fieldset creation

tests/test_constructors.py

@@ -0,0 +1,19 @@
+import plasticparcels as pp
+import parcels
+from datetime import datetime, timedelta
+
+def test_create_fieldset():
+    settings_file = 'tests/test_data/test_settings.json'
+    settings = pp.utils.load_settings(settings_file)
+    settings = pp.utils.download_plasticparcels_dataset('NEMO0083', settings, 'input_data')
+
+    settings['simulation'] = {'startdate': datetime.strptime('2020-01-04-00:00:00', '%Y-%m-%d-%H:%M:%S'), # Start date of simulation
+                                'runtime': timedelta(days=2),        # Runtime of simulation
+                                'outputdt': timedelta(hours=1),      # Timestep of output
+                                'dt': timedelta(minutes=20),          # Timestep of advection
+                                }
+
+    fieldset = pp.constructors.create_fieldset(settings)
+
+    assert isinstance(fieldset, parcels.FieldSet)
+