Add support for custom unfixable error messages

[Andreas]

What is the problem you're trying to solve?

My plugin supports to customize unfixable error messages.

But testing them with always fails

{
  fix: true,
  reject: [{
    unfixable: true,
    message: "This message passes first assertion, but alwys fail the one below",
  }]

What solution would you like to see?

Would it make sense to assert following only if unfixable is falsy?

jest-preset-stylelint/getTestRule.js

Lines 116 to 125 in 682eb61

 // Checks whether only errors other than those fixed are reported 
 const outputAfterLintOnFixedCode = await lint({ 
 	...stylelintOptions, 
 	code: fixedCode, 
 }); 
  
 expect(outputAfterLintOnFixedCode.results[0]).toMatchObject({ 
 	warnings: outputAfterFix.results[0].warnings, 
 	parseErrors: [], 
 });