Remix stub doesn't transition through loading state after form submission

[jabrks]

Reproduction

Visit https://stackblitz.com/edit/remix-run-remix-zgfwmo?file=app%2Ftests%2F_index.spec.tsx&view=editor and observe the failing test.

Compare that with the same code running in a real browser environment, which behaves as expected

System Info

System:
  OS: macOS 15.1
  CPU: (10) arm64 Apple M1 Pro
  Memory: 881.70 MB / 32.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 20.17.0 - ~/.nvm/versions/node/v20.17.0/bin/node
  npm: 10.9.0 - ~/.nvm/versions/node/v20.17.0/bin/npm
  bun: 1.0.14 - ~/.bun/bin/bun
Browsers:
  Chrome: 130.0.6723.117
  Chrome Canary: 132.0.6797.0
  Safari: 18.1
npmPackages:
  @remix-run/dev: ^2.14.0 => 2.14.0 
  @remix-run/express: ^2.14.0 => 2.14.0 
  @remix-run/node: ^2.14.0 => 2.14.0 
  @remix-run/react: ^2.14.0 => 2.14.0 
  @remix-run/testing: ^2.14.0 => 2.14.0 
  vite: ^5.4.11 => 5.4.11

Used Package Manager

npm

Expected Behavior

The form submission should transition through these states

idle → submitting → loading → idle

Actual Behavior

The form submission does not transition through the loading state

idle → submitting → idle