Only run tests directly in __tests__

This lets us share code between test files by placing them in __tests__/utils.

Author: gaearon

scripts/jest/config.source.js

@@ -10,7 +10,8 @@ module.exports = {
   },
   setupFiles: [require.resolve('./setupEnvironment.js')],
   setupTestFrameworkScriptFile: require.resolve('./setupTests.js'),
-  testRegex: '/__tests__/.*(\\.js|\\.coffee|[^d]\\.ts)$',
+  // Only include files directly in __tests__, not in nested folders.
+  testRegex: '/__tests__/[^/]*(\\.js|\\.coffee|[^d]\\.ts)$',
   moduleFileExtensions: ['js', 'json', 'node', 'coffee', 'ts'],
   rootDir: process.cwd(),
   roots: ['<rootDir>/packages', '<rootDir>/scripts'],