3.0.8 Multipart PATCH requests fail in minitest(Rack::Multipart::EmptyContentError)

[kochetkovandrew]

POST requests work:

      post :create, params: {
        attachment: {
          attachment: fixture_file_upload('fixture_file.json', 'text/plain')
        }
      }

But the following PATCH request raises an exception
Minitest::UnexpectedError: ActionController::BadRequest: Invalid request parameters: Rack::Multipart::EmptyContentError

    patch :update, params: {
      id: attachment_id,
      attachment: {
        attachment: fixture_file_upload('fixture_file.json', 'text/plain')
      }
    }

At the same time it works from browser:

@headers="Content-Disposition: form-data; name=\"attachment[attachment]\"; filename=\"fixture_file.json\"\r\nContent-Type: text/plain\r\n">}

But doesn't work from minitest:
@headers="content-disposition: form-data; name=\"attachment[attachment]\"; filename=\"fixture_file.json\"\r\ncontent-type: text/plain\r\ncontent-length: 203\r\n">}

The only differences I can find were capitalized Content-* header names and presence of content-length in minitest request headers (content-length 203 corresponds to the real size of the file). Changing of text/plain to application/json or application/octet-stream had no effect.

Downgrading to rack 2.2.8 solves the issue.
Rails 7.1.2, minitest 5.20.0

[jeremyevans]

Where do the post and patch methods come from? They aren't in minitest or rack. Maybe in rack-test? Are you using an old version of rack-test (before rack-test 2.0.0)?

Can you post a minimal self contained example showing the problem?