STINNER Victor wrote:
> I don't understand the link between third party extensions and
> test_getargs2. test_getargs2 is a unit test for non-regression of
> CPython. Can you please elaborate?

A test failure needs a broken buffer provider that hands out a non-contiguous
buffer in response to a PyBUF_SIMPLE request.

The only non-contiguous buffer provider in the stdlib is memoryview.
If I break memoryview's getbufferproc ...

diff --git a/Objects/memoryobject.c b/Objects/memoryobject.c
--- a/Objects/memoryobject.c
+++ b/Objects/memoryobject.c
@@ -1465,11 +1465,6 @@
         return -1;
     }
     if (!REQ_STRIDES(flags)) {
-        if (!MV_C_CONTIGUOUS(baseflags)) {
-            PyErr_SetString(PyExc_BufferError,
-                "memoryview: underlying buffer is not C-contiguous");
-            return -1;
-        }
         view->strides = NULL;
     }
     if (!REQ_SHAPE(flags)) {

...

test_buffer already fails.  So what should I test?  Perhaps ctypes has
some capabilities that I'm unaware of.

If I'm using _testbuffer.ndarray(), I'm effectively testing that the
getbufferproc of ndarray is correct (which is also tested multiple times
in test_buffer).