Add regression test to avoid helper init bug again

Author: rpep

tests/test_regression_init_scalar.py

@@ -0,0 +1,26 @@
+import unittest
+
+
+def regression_helper_init_scalar():
+    import fidimag
+    import numpy as np
+    # Create simulation
+    mesh = fidimag.common.CuboidMesh(nx=10, ny=2, nz=1,
+                                     dx=1, dy=1, dz=1)
+    sim = fidimag.atomistic.Sim(mesh)
+    # Set the magnetisation and save it to mu_s.npy
+    sim.mu_s = 3
+    np.save('mu_s.npy', sim.mu_s)
+
+    # Create another simulation with less elements in the x direction
+    mesh2 = fidimag.common.CuboidMesh(nx=5, ny=2, nz=1,
+                                      dx=1, dy=1, dz=1)
+    sim2 = fidimag.atomistic.Sim(mesh2)
+    # Set the magnetisation loading the other simulation file
+    sim2.mu_s = np.load('mu_s.npy')
+
+
+class regression_test(unittest.TestCase):
+
+    def test_init_scalar(self):
+        self.assertRaises(ValueError, regression_helper_init_scalar)