fix(jest-next.js): rectify broken jest moduleNameMapper configuration

close #815
issue vercel/next.js#35634
issue vercel/next.js#36312

jest.config.js

@@ -2,10 +2,6 @@ const { pathsToModuleNameMapper } = require('ts-jest');
 const { compilerOptions } = require('./tsconfig.json');
 const nextJest = require('next/jest');
 
-const paths = pathsToModuleNameMapper(compilerOptions.paths, {
-  prefix: '<rootDir>/',
-});
-
 /** @type {import('ts-jest').InitialOptionsTsJest} */
 const customJestConfig = {
   collectCoverage: true,
@@ -26,9 +22,6 @@ const customJestConfig = {
     '!**/Header.tsx',
   ],
   moduleDirectories: ['node_modules', '<rootDir>/'],
-  moduleNameMapper: {
-    ...paths,
-  },
   setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
   testEnvironment: 'jest-environment-jsdom',
 };
@@ -38,13 +31,26 @@ const createJestConfig = nextJest({
 })(customJestConfig);
 
 module.exports = async () => {
+  // Create Next.js jest configuration presets
   const jestConfig = await createJestConfig();
+
+  // Custom `moduleNameMapper` configuration
+  const paths = pathsToModuleNameMapper(compilerOptions.paths, {
+    prefix: '<rootDir>/',
+  });
+  const moduleNameMapper = {
+    ...jestConfig.moduleNameMapper,
+    ...paths,
+  };
+
+  // Custom `transformIgnorePatterns` configuration
   const transformIgnorePatterns = [
     // Transform ESM-only modules in `node_modules`.
     '/node_modules/(?!next-mdx-remote|@mdx-js|@react-hook)',
     ...jestConfig.transformIgnorePatterns.filter(
       pattern => pattern !== '/node_modules/'
     ),
   ];
-  return { ...jestConfig, transformIgnorePatterns };
+
+  return { ...jestConfig, moduleNameMapper, transformIgnorePatterns };
 };