Add proof of concept test for cpu.update_magnetic

tests/test_update_functions.py

@@ -0,0 +1,40 @@
+import numpy as np
+
+from gprMax import config
+from gprMax.grid import FDTDGrid
+from gprMax.updates import CPUUpdates
+
+
+class MockSimulationConfig:
+    dtypes = {"float_or_double": np.float32}
+
+
+class MockModelConfig:
+    ompthreads = 1
+
+
+def test_update_magnetic_cpu(monkeypatch):
+    monkeypatch.setattr(config, "sim_config", MockSimulationConfig)
+    monkeypatch.setattr(config, "get_model_config", MockModelConfig)
+
+    # TODO: Move building the grid into a fixture
+    grid = FDTDGrid()
+    grid.nx = 100
+    grid.ny = 100
+    grid.nz = 100
+    grid.initialise_geometry_arrays()
+    grid.initialise_field_arrays()
+    grid.initialise_std_update_coeff_arrays()
+
+    cpu_updates = CPUUpdates(grid)
+
+    expected_value = grid.Ex.copy()
+
+    cpu_updates.update_magnetic()
+
+    assert np.equal(grid.Ex, expected_value).all()
+    assert np.equal(grid.Ey, expected_value).all()
+    assert np.equal(grid.Ez, expected_value).all()
+    assert np.equal(grid.Hx, expected_value).all()
+    assert np.equal(grid.Hy, expected_value).all()
+    assert np.equal(grid.Hz, expected_value).all()