Honor only relative NODE_PATH

@see facebook#1194

Author: Enoah Netzach

Diff for: packages/react-scripts/utils/createJestConfig.js

@@ -9,13 +9,14 @@
 
 // Note: this file does not exist after ejecting.
 
-const pathExists = require('path-exists');
+const fs = require('fs');
+const path = require('path');
 const paths = require('../config/paths');
 
 module.exports = (resolve, rootDir, isEjecting) => {
   // Use this instead of `paths.testsSetup` to avoid putting
   // an absolute filename into configuration after ejecting.
-  const setupTestsFile = pathExists.sync(paths.testsSetup) ? '<rootDir>/src/setupTests.js' : undefined;
+  const setupTestsFile = fs.existsSync(paths.testsSetup) ? '<rootDir>/src/setupTests.js' : undefined;
 
   // TODO: I don't know if it's safe or not to just use / as path separator
   // in Jest configs. We need help from somebody with Windows to determine this.
@@ -38,7 +39,9 @@ module.exports = (resolve, rootDir, isEjecting) => {
     transformIgnorePatterns: [
       '[/\\\\]node_modules[/\\\\].+\\.(js|jsx)$'
     ],
-    moduleDirectories: ['node_modules', process.env.NODE_PATH].filter(dir => dir),
+    moduleDirectories: ['node_modules', process.env.NODE_PATH]
+      .filter(dir => dir)
+      .filter(folder => !path.isAbsolute(folder)),
     moduleNameMapper: {
       '^react-native$': 'react-native-web'
     }