Multiple headers with the same name gets replaced in test client

[LukeMarlin]

werkzeug.Headers allows to add multiple headers with the same name:

from werkzeug import Headers
h = Headers()
h.add("example", "value1")
h.add("example", "value2")
h.get_all("example")
> ['value1', 'value2']

Trying to write a test case to gracefully prevent users from doing so with a custom header, I noticed that when using werkzeug's TestClient and issuing a get, the request.headers context only receive the latest value, not both.

It seems that this is due to

werkzeug/src/werkzeug/test.py

Lines 743 to 744 in e7ba08f

	for key, value in headers.to_wsgi_list():
	result["HTTP_%s" % key.upper().replace("-", "_")] = value

Should these be modified to preserve all values instead of replacing them?
I'd gladly change it if it makes sense.

[davidism]

The problem is that to_wsgi_list is not really intended for creating the WSGI environ, it's for creating the header lines to write out in WSGI's start_response.

In the environ, there will be only one value for each header, which will be joined using the appropriate HTTP continuation.

[LukeMarlin]

@davidism Thank you for the answer.
However, I'm not sure what to think about it. Is there a possible fix? Is it desirable?
If you have some pointers, I might give it a try