What & Why

• Now, jest-preview hasn't implemented getCacheKey for css, file and fileCRA transformer.
  

  jest-preview/src/preconfigTransform/css.ts

  Lines 1 to 8 in 6ce35ca

  	'use strict';
  	import { processCss } from '../transform';
  	function process(src: string, filename: string) {
  	return processCss(src, filename);
  	}
  	export default { process };

• The reason is that we are not very deeply understand the benefit of getCacheKey. The [docs]((https://jestjs.io/docs/code-transformation) itself is not very detail. But we know it boosts the performance when running Jest since we're caching the transformed files.

How

• We can find @swc/jest implemented getCacheKey. Let's see how they do that.
  https://github.com/swc-project/jest/blob/17cf883b46c050a485975d8ce96a05277cf6032f/index.ts#L37-L52
• There are some related PRs as well Implement getCacheKey swc-project/jest#32 feat: add support for async transform swc-project/jest#76
• We need to benchmark to see how much users' time getCacheKey saves.