synthetic surface and spm specific features

tests/node_tests/mfm_current.py

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+import numpy as np
+import pytest
+from tests.node_tests._shared import make_field
+
+
+def test_output_shapes():
+    from backend.nodes.mfm_current import MFMCurrentSimulation
+
+    node = MFMCurrentSimulation()
+    field = make_field(shape=(32, 32))
+
+    hx, hz, force = node.process(field, height=100e-9, current=1e-3,
+                                 width=100e-9, tip_magnetization=1e5)
+
+    assert hx.data.shape == (32, 32)
+    assert hz.data.shape == (32, 32)
+    assert force.data.shape == (32, 32)
+
+
+def test_finite_values():
+    from backend.nodes.mfm_current import MFMCurrentSimulation
+
+    node = MFMCurrentSimulation()
+    field = make_field(shape=(64, 64))
+
+    hx, hz, force = node.process(field, height=100e-9, current=1e-3,
+                                 width=100e-9, tip_magnetization=1e5)
+
+    assert np.isfinite(hx.data).all()
+    assert np.isfinite(hz.data).all()
+    assert np.isfinite(force.data).all()
+
+
+def test_hz_antisymmetric():
+    from backend.nodes.mfm_current import MFMCurrentSimulation
+
+    node = MFMCurrentSimulation()
+    # Use even grid so centre falls between pixels symmetrically
+    field = make_field(shape=(16, 64), xreal=1e-6, yreal=1e-6)
+
+    _, hz, _ = node.process(field, height=100e-9, current=1e-3,
+                            width=100e-9, tip_magnetization=1e5)
+
+    hz_row = hz.data[0, :]
+    n = len(hz_row)
+    # The x-grid uses linspace(0, xreal, n, endpoint=False) - xreal/2,
+    # so x[i] + x[n-i] == 0 for i in 1..n-1.
+    # Hz should be antisymmetric about x=0: Hz(x) ≈ -Hz(-x)
+    for i in range(1, n // 2):
+        left = hz_row[i]
+        right = hz_row[n - i]
+        assert np.sign(left) == -np.sign(right), (
+            f"Hz not antisymmetric at positions {i} and {n - i}: "
+            f"{left} vs {right}"
+        )
+        np.testing.assert_allclose(left, -right, rtol=1e-10)
+
+
+def test_units():
+    from backend.nodes.mfm_current import MFMCurrentSimulation
+
+    node = MFMCurrentSimulation()
+    field = make_field(shape=(32, 32))
+
+    hx, hz, force = node.process(field, height=100e-9, current=1e-3,
+                                 width=100e-9, tip_magnetization=1e5)
+
+    assert hx.si_unit_z == "A/m"
+    assert hz.si_unit_z == "A/m"
+    assert force.si_unit_z == "N"