Components styled with emotion do not get theme from material theme provider

[Alexander Droll]

Describe the bug

Having a react app using material ui and emotion/styled, components styled with emotion/styled do not receive the theme from the material ui ThemeProvider in tests.
This is working for production code.

As a workaround one could wrap the tested component into an additional theme provider from emotions. See also this stack overflow discussion.

Reproduction

A minimal example can be found in this StackBlitz sandbox

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.18.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @vitejs/plugin-react: ^4.2.1 => 4.2.1 
    @vitest/ui: 1.5.3 => 1.5.3 
    vite: 5.2.10 => 5.2.10 
    vitest: 1.5.3 => 1.5.3

Used Package Manager

npm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[Hiroshi Ogawa]

As indicated by the warning:

stderr | node_modules/@ emotion/react/dist/emotion-react.esm.js:472:15
You are loading @emotion/react when it is already loaded. Running multiple instances may cause problems. This can happen if multiple versions are used, or if multiple builds of the same version are used.

this is a dual package issue of @emotion/react. The one imported through @mui/material (via NodeJS) and the other from your source code (via Vite/Vitest) are seeing different context singleton.

It looks like NodeJS is loading @emotion/react/dist/emotion-react.cjs.mjs, so you can force Vitest's resolution via alias:
https://stackblitz.com/edit/vitest-dev-vitest-wpfmsa?file=vitest.config.ts

  test: {
    alias: {
      '@emotion/react': path.resolve(
        'node_modules/@emotion/react/dist/emotion-react.cjs.mjs'
      ),
    },
  },

Looking at https://publint.dev/@emotion/react@11.11.4, the package exports is quite complicated, but seems legitimate, so it might be possible that Vite / Vitest's default resolution is doing something wrong.

[Alexander Droll]

Well as workaround this works but I think it is not good that vite and vitest behave in a different way.
Isn't there a way to force the loading of the correct module on vitest side?

[Hiroshi Ogawa]

I tried to decipher what's happening but unfortunately I couldn't figure out yet where this goes wrong. https://github.com/hi-ogawa/reproductions/tree/main/vitest-5664-mui-emotion-provider

It seems like Vite SSR is fine, so Vitest / Vite-node might be making bad resolution. It could be a bug, so we can leave this issue open.