[Bug] Storybook environment variables not fully supported in Vitest plugin

[vanessayuenn]

By default, Storybook only reads env variables prefixed with STORYBOOK_ (and VITE_ for Vite projects), and if you want it to read more variables, you have to specify it in main.js

// .storybook/main.js
export default {
  env: (config) => ({
    ...config,
    EXAMPLE_VAR: 'An environment variable configured in Storybook',
  }),
};

In Vitest with the Storybook plugin, on the other hand, it only takes VITE_ variables into consideration. Also, it will not know about that extra env passed from main.js.

💡 Solutions/Action items:

• Make the plugin handle STORYBOOK_ variables by default
• Make the plugin smarter and merge the env config from main.js with the env config from Vitest