Test: Numpy Scalar Creation (#1530)

I found that the numpy array tests already contained an empty-shaped
array test, but none with data in it.

Following PEP 3118, scalars have an empty shape and ndim 0. This
works already and is now also documented/covered by a test.
diff --git a/tests/test_numpy_array.py b/tests/test_numpy_array.py
index 8ac0e66..8bacb7f 100644
--- a/tests/test_numpy_array.py
+++ b/tests/test_numpy_array.py
@@ -138,6 +138,11 @@
 def test_make_empty_shaped_array():
     m.make_empty_shaped_array()
 
+    # empty shape means numpy scalar, PEP 3118
+    assert m.scalar_int().ndim == 0
+    assert m.scalar_int().shape == ()
+    assert m.scalar_int() == 42
+
 
 def test_wrap():
     def assert_references(a, b, base=None):