only-changed-jest-watch-plugin/example/a.test.js

Jest watch plugin for running either only the modified test (for TDD), or tests of dependant modules

const a = require('./a');

test('adds 2 + 1 to equal 3 and 2 - 1 to equal 1', () => {
  expect(a(2, 1)).toEqual([3,1]);
});