MultiPartException('Missing boundary in multipart.') using test_client() on "multipart/form-data" API content

[alanbchristie]

Description

I'm using connexion (v3.1.0) in unit testing. I have an API endpoint that uses content that multipart/form-data content. In connexion v2 (v2.14.2) this was possible. In connexion v3 I appear to be unable to test these endpoints without encountering a MultiPartException('Missing boundary in multipart.') ERROR.

For more details you can see connexion discussion 1964.

Expected behaviour

I should be able to use the test_client() to test APIs with multipart/form-data content. This might be a problem with connexion or starlette, it's certainly not something the test should need to be responsible for - after all the content tells the test client what's expected - I present data (in a Dictionary) - the test client adjusts it to satisfy the defined content for the API being tested.

Actual behaviour

I get an exception: -

ERROR    connexion.middleware.exceptions:exceptions.py:108 MultiPartException('Missing boundary in multipart.')

Steps to reproduce

See connexion discussion 1964.

Additional info:

Output of the commands:

• python --version (Python 3.12.4)
• pip show connexion | grep "^Version\:" (Version: 3.1.0)