fix normal tests in namespace, expression

Two unittests where the normal in (namespace) expressions is being tested
incorrectly uses the dimension of the volume instead of the boundary. This
patch fixes the problem by explicitly defining the dimension to lower for.

tests/test_function.py

@@ -672,7 +672,7 @@ def test_d_arg(self):
   def test_n(self):
     ns = function.Namespace()
     topo, ns.x = mesh.rectilinear([1])
-    self.assertEqualLowered(ns.eval_i('n(x_i)'), function.normal(ns.x), ndims=topo.ndims)
+    self.assertEqualLowered(ns.eval_i('n(x_i)'), function.normal(ns.x), ndims=topo.ndims-1)
 
   def test_functions(self):
     def sqr(a):
@@ -738,8 +738,8 @@ def setUp(self):
     self.ns.a32 = numpy.array([[1,2],[3,4],[5,6]])
     self.x = function.Argument('x',())
 
-  def assertEqualLowered(self, s, f):
-    self.assertEqual((s @ self.ns).prepare_eval(ndims=2).simplified, f.prepare_eval(ndims=2).simplified)
+  def assertEqualLowered(self, s, f, *, ndims=2):
+    self.assertEqual((s @ self.ns).prepare_eval(ndims=ndims).simplified, f.prepare_eval(ndims=ndims).simplified)
 
   def test_group(self): self.assertEqualLowered('(a)', self.ns.a)
   def test_arg(self): self.assertEqualLowered('a2_i ?x_i', function.dot(self.ns.a2, function.Argument('x', [2]), axes=[0]))
@@ -748,7 +748,7 @@ def test_multisubstitute(self): self.assertEqualLowered('(a2_i + ?x_i + ?y_i)(x_
   def test_call(self): self.assertEqualLowered('sin(a)', function.sin(self.ns.a))
   def test_call2(self): self.assertEqual(self.ns.eval_ij('arctan2(a2_i, a3_j)').prepare_eval(ndims=2).simplified, function.arctan2(self.ns.a2[:,None], self.ns.a3[None,:]).prepare_eval(ndims=2).simplified)
   def test_eye(self): self.assertEqualLowered('δ_ij a2_i', function.dot(function.eye(2), self.ns.a2, axes=[0]))
-  def test_normal(self): self.assertEqualLowered('n_i', self.ns.x.normal())
+  def test_normal(self): self.assertEqualLowered('n_i', self.ns.x.normal(), ndims=1)
   def test_getitem(self): self.assertEqualLowered('a2_0', self.ns.a2[0])
   def test_trace(self): self.assertEqualLowered('a22_ii', function.trace(self.ns.a22, 0, 1))
   def test_sum(self): self.assertEqualLowered('a2_i a2_i', function.sum(self.ns.a2 * self.ns.a2, axis=0))