I am working on a compiler that generates JavaScript modules and their associated type declarations: it takes one source with a specific grammar and output 3 different files:

1. a ESM implementation
2. a CJS implementation
3. A type declaration

Those files export a class with a bunch of methods (that's an example of the type definition that's being generated):

export default class MyClass extends Base {
  myApi1(): Promise<void>;
  getFoo(): Promise<string>;
  // ...
}

All those files are generated by the compiler itself and I am wondering what would good testing strategies to satisfy the following criteria:

• JS modules are valid JS files
• The type declaration is a valid TS file
• All files don't have extra/missing imports
• That the generated types are corrects (methods have correct arg and return types)
• Tests can be run in CI and be as fast as possible
• Tests are as reliable as possible

More broadly my question is how to test generated files from a compiler/transpiler when those aren't bytecode?