Chore: Make betterer tests more stable (#51703)

* rewrite eslint test to not care about position of errors

* changing file contents shouldn't require a betterer.results update

* fix up eslint test

* fix the undocumented stories test

* ignore .test.ts files as well

.betterer.ts

@@ -1,28 +1,18 @@
 import { regexp } from '@betterer/regexp';
-import { eslint } from '@betterer/eslint';
 import { BettererFileTest } from '@betterer/betterer';
+import { ESLint, Linter } from 'eslint';
+import { existsSync } from 'fs';
 
 export default {
   'no enzyme tests': () => regexp(/from 'enzyme'/g).include('**/*.test.*'),
-  'better eslint': () =>
-    eslint({
-      '@typescript-eslint/no-explicit-any': 'error',
-      '@typescript-eslint/consistent-type-assertions': [
-        'error',
-        {
-          assertionStyle: 'never',
-        },
-      ],
-    }).include('**/*.{ts,tsx}'),
-  'no undocumented stories': () => countUndocumentedStories().include('**/*.{story.tsx,mdx}'),
+  'better eslint': () => countEslintErrors().include('**/*.{ts,tsx}'),
+  'no undocumented stories': () => countUndocumentedStories().include('**/*.story.tsx'),
 };
 
 function countUndocumentedStories() {
   return new BettererFileTest(async (filePaths, fileTestResult) => {
-    const storyFilePaths = filePaths.filter((filePath) => filePath.endsWith('story.tsx'));
-    const mdxFilePaths = filePaths.filter((filePath) => filePath.endsWith('mdx'));
-    storyFilePaths.forEach((filePath) => {
-      if (!mdxFilePaths.includes(filePath.replace(/\.story.tsx$/, '.mdx'))) {
+    filePaths.forEach((filePath) => {
+      if (!existsSync(filePath.replace(/\.story.tsx$/, '.mdx'))) {
         // In this case the file contents don't matter:
         const file = fileTestResult.addFile(filePath, '');
         // Add the issue to the first character of the file:
@@ -31,3 +21,49 @@ function countUndocumentedStories() {
     });
   });
 }
+
+function countEslintErrors() {
+  return new BettererFileTest(async (filePaths, fileTestResult, resolver) => {
+    const { baseDirectory } = resolver;
+    const cli = new ESLint({ cwd: baseDirectory });
+
+    await Promise.all(
+      filePaths.map(async (filePath) => {
+        const linterOptions = (await cli.calculateConfigForFile(filePath)) as Linter.Config;
+
+        const rules: Partial<Linter.RulesRecord> = {
+          '@typescript-eslint/no-explicit-any': 'error',
+        };
+
+        if (!filePath.endsWith('.test.tsx') && !filePath.endsWith('.test.ts')) {
+          rules['@typescript-eslint/consistent-type-assertions'] = [
+            'error',
+            {
+              assertionStyle: 'never',
+            },
+          ];
+        }
+
+        const runner = new ESLint({
+          baseConfig: {
+            ...linterOptions,
+            rules,
+          },
+          useEslintrc: false,
+          cwd: baseDirectory,
+        });
+
+        const lintResults = await runner.lintFiles([filePath]);
+        lintResults
+          .filter((lintResult) => lintResult.source)
+          .forEach((lintResult) => {
+            const { messages } = lintResult;
+            const file = fileTestResult.addFile(filePath, '');
+            messages.forEach((message, index) => {
+              file.addIssue(0, 0, message.message, `${index}`);
+            });
+          });
+      })
+    );
+  });
+}