Add docstring to matmul

tests/test_ThermalExpansion.py

@@ -6,19 +6,21 @@
 coeff = np.array([[11, 12, 13], [12, 22, 23], [13, 23, 33]])
 alpha = ThEx(coeff)
 
-class MyTestCase(unittest.TestCase):
+class TestThermalExpansion(unittest.TestCase):
     def test_constructor_isotropic(self):
         coeff = 23e-6
         alpha = ThEx.isotropic(coeff)
-        eps = alpha * 1.0
-        np.testing.assert_almost_equal(eps.matrix, np.eye(3)*coeff)
+        temp = 25
+        eps = alpha * temp
+        np.testing.assert_almost_equal(eps.matrix, np.eye(3) * coeff * temp)
 
     def test_monoclinic_mul(self):
         n=50
         rotations = Rotation.random(n)
         alphas = alpha * rotations
         temp = np.linspace(0,10,n)
         eps = alphas * temp
+        assert eps.shape == (n,)
         for i in range(n):
             rot_mat = rotations[i].as_matrix()
             rotated_strain_matrix = np.matmul(rot_mat.T, np.matmul(coeff, rot_mat)) * temp[i]