WTF Jest

jest-fix.js

var origExpect = global.expect;
global.expect = function (subject) {
    if (arguments.length > 1) {
        throw new Error('You passed more than one argument to jest expect.');
    }
    return origExpect(subject);
};

package.json

{
  "name": "wtf-jest",
  "private": true,
  "devDependencies": {
    "jest": "20.0.4",
    "unexpected": "10.33.1"
  },
  "jest": {
    "setupTestFrameworkScriptFile": "./jest-fix"
  }
}

wtf-jest.spec.js

// this test will pass with jest expect, as it just silently ignores other
// args. it will fail with the jest-fix file loaded

it('should be unexpected', () => {
    expect(true, 'to be false');
});