Django JsonResponse returning content-type text/html instead of application/json
It appears that
self.client.get('/api/list')
led to an error-page (hence the text/html content_type).
EDIT: Not an error-page, but an http-redirect, according to LudwikTrammer.
Changing
self.client.get('/api/list')
to
self.client.get('/api/list/')
solved the issue.