Add subtests to demonstrate processing Python buffer protocol objects…

… with step > 1

tests/test_stl_binders.py

@@ -84,6 +84,10 @@ def test_vector_buffer():
         mv[2] = '\x06'
     assert v[2] == 6
 
+    mv = memoryview(b)
+    v = m.VectorUChar(mv[::2])
+    assert v[1] == 3
+
     with pytest.raises(RuntimeError) as excinfo:
         m.create_undeclstruct()  # Undeclared struct contents, no buffer interface
     assert "NumPy type info missing for " in str(excinfo.value)
@@ -118,6 +122,10 @@ def test_vector_buffer_numpy():
                                                    ('y', 'float64'), ('z', 'bool')], align=True)))
     assert len(v) == 3
 
+    b = np.array([1, 2, 3, 4], dtype=np.uint8)
+    v = m.VectorUChar(b[::2])
+    assert v[1] == 3
+
 
 def test_vector_bool():
     import pybind11_cross_module_tests as cm