draw function snapshot testing

[TheTallJerry]

• Sets up Jest testing environment.
• Adds a seed configuration, as per https://github.com/rough-stuff/rough/wiki#seed.
• Adds a snapshot test for the main draw function, testing an exact same generated SVG should the seed be provided.

[david-yz-liu]

Great work, @TheTallJerry!

[david-yz-liu]

The two imports are inconsistent, and they shouldn't need to be. You can import both MemoryModel and draw from ../src/index, as that file exports both of them. (Not sure if importing from index.js is special in some way.)

[TheTallJerry]

This evolved into something larger. Essentially, the new import now looks like

import exports from "../src";
const { MemoryModel, draw } = exports;

which is valid syntax (and cleaner) outside of this context. However, it appears that RoughJS relies on ESM exports, which Jest has confirmed that it won't support. This comes into play with the draw function as it eventually calls RoughJS.

As a result, with this setup, Jest reports an error along the lines of Unexpected token export. This is fixed by forcing a manual resolve with Jest, as mentioned on stackoverflow and specifically this comment. The updated Jest config now has

  moduleNameMapper: {
    // Force module roughjs to resolve with the CJS entry point, because Jest does not support package.json.exports. Elaborated in PR#15.
    "roughjs": require.resolve('roughjs'),
  },

If Jest at some point supports ESM, or if RoughJS gets updated to be compatible with Jest in this aspect, then this configuration can be removed. As shown above, I left a comment alongside the config for future reference.

[TheTallJerry]

Related: because MemoryModel is exported as a class and then dynamically imported, in order to use it as a type, I had to use InstanceType<typeof MemoryModel> instead of simply MemoryModel. See this stackoverflow comment for more elaboration.

[david-yz-liu]

Great work, thank you @TheTallJerry!