The following error can occur using Jest:
Using Jest CLI v13.2.3, jasmine2 FAIL dist\__tests__\import-editions-test.js (0s) ● Runtime Error - SyntaxError: Identifier 'jest' has already been declared in file 'dist\__tests__\import-editions-test.js'. Make sure your preprocessor is set up correctly and ensure your 'preprocessorIgnorePatterns' configuration is correct: http://facebook.github.io/jest/docs/api.html#preprocessorignorepatterns-array-string If you are currently setting up Jest or modifying your preprocessor, try `jest --no-cache`. Preprocessor: No preprocessor specified, consider installing 'babel-jest'. Jest tried to the execute the following code: "use strict"; const import_editions_1 = require('../import-editions'); const jest = require('jest'); jest.unmock('../import-editions'); describe('parseLine', () => { it('parses the header part of the line', () => { expect(import_editions_1.parseLine('abc')).toBe('abc'); }); }); at Runtime._runSourceText (node_modules\jest-runtime\build\index.js:410:15) at Runtime._execModule (node_modules\jest-runtime\build\index.js:374:30) at Runtime.requireModule (node_modules\jest-runtime\build\index.js:210:14) at jasmine2 (node_modules\jest-jasmine2\build\index.js:293:11) at Test.run (node_modules\jest-cli\build\Test.js:50:12) at promise.then.then.data (node_modules\jest-cli\build\TestRunner.js:264:62) 1 test suite failed, 0 tests passed (0 total in 1 test suite, run time 1.086s) npm ERR! Test failed. See above for more details.
This indicates that you tried to import Jest into your file – it is implicitly added for you as a global when you run tests. So, don’t do this:
const jest = require('jest');