more setitem into unrealized tests (#14737)

* more setitem into unrealized tests

into empty, const with alu, and arange

* typo

test/backend/test_setitem.py

@@ -69,10 +69,31 @@ class TestSetitem(unittest.TestCase):
     t = Tensor.zeros(6, dtype=dtypes.float).contiguous().realize()
     with self.assertRaises(RuntimeError): t[2:4] = Tensor([1, 2], dtype=dtypes.int)
 
-  def test_setitem_into_noncontiguous(self):
+  def test_setitem_into_empty(self):
+    t = Tensor.empty(4)
+    t[1] = 5
+    self.assertEqual(t[1].item(), 5)
+
+  def test_setitem_into_cont(self):
     t = Tensor.ones(4)
     with self.assertRaises(RuntimeError): t[1] = 5
 
+  def test_setitem_into_const_alu(self):
+    # TODO: this is not consistent
+    t = Tensor.ones(4) + Tensor.ones(4)
+    t[1] = 5
+    self.assertListEqual(t.tolist(), [2, 5, 2, 2])
+
+    t = Tensor.ones(4) + Tensor.ones(4)
+    t.realize()
+    with self.assertRaises(RuntimeError): t[1] = 5
+
+  def test_setitem_into_arange(self):
+    # NOTE: arange has no real buffer, but assigning to it is fine
+    t = Tensor.arange(4)
+    t[1] = 5
+    self.assertListEqual(t.tolist(), [0, 5, 2, 3])
+
   def test_setitem_chained_indexing(self):
     # N[i][j] must work the same as N[i, j]
     N1 = Tensor.zeros((3, 3)).contiguous().realize()