Refactor AdvectionRK45 kernel selection into dedicated util

Author: VeckoTheGecko

tests/test_particleset_execute.py

@@ -26,6 +26,7 @@
 from parcels.interpolators import UXPiecewiseConstantFace, UXPiecewiseLinearNode, XLinear
 from parcels.kernels import AdvectionEE, AdvectionRK2, AdvectionRK4, AdvectionRK4_3D, AdvectionRK45
 from tests.common_kernels import DoNothing
+from tests.utils import DEFAULT_PARTICLES
 
 
 @pytest.fixture
@@ -166,12 +167,7 @@ def test_particleset_run_RK_to_endtime_fwd_bwd(fieldset, kernel, dt):
     fieldset.U.data[:] = 0.0
     fieldset.V.data[:] = 0.0
 
-    if kernel == AdvectionRK45:
-        MyParticle = Particle.add_variable(Variable("next_dt"))
-    else:
-        MyParticle = Particle
-
-    pset = ParticleSet(fieldset, pclass=MyParticle, lon=[0.2], lat=[5.0], time=[starttime])
+    pset = ParticleSet(fieldset, pclass=DEFAULT_PARTICLES[kernel], lon=[0.2], lat=[5.0], time=[starttime])
     pset.execute(kernel, endtime=endtime, dt=dt)
     assert pset[0].time == fieldset.time_interval.time_length_as_flt
 

tests/utils.py

@@ -3,13 +3,14 @@
 from __future__ import annotations
 
 import struct
+from collections import defaultdict
 from pathlib import Path
 
 import numpy as np
 import xarray as xr
 
 import parcels
-from parcels import Field, FieldSet, VectorField
+from parcels import Field, FieldSet, Particle, Variable, VectorField
 from parcels._core.xgrid import _FIELD_DATA_ORDERING, XGrid, get_axis_from_dim_name
 from parcels._datasets.structured.generated import simple_UV_dataset
 from parcels.interpolators import XLinear
@@ -18,6 +19,10 @@
 TEST_ROOT = PROJECT_ROOT / "tests"
 TEST_DATA = TEST_ROOT / "test_data"
 
+# Define default particle classes for different built-in kernels
+DEFAULT_PARTICLES = defaultdict(lambda: Particle)
+DEFAULT_PARTICLES[parcels.kernels.AdvectionRK45] = Particle.add_variable(Variable("next_dt"))
+
 
 def create_fieldset_unit_mesh(xdim=20, ydim=20, mesh="flat") -> FieldSet:
     """Standard unit mesh fieldset with U and V equivalent to longitude and latitude."""