JavaScript: refactoring legacy functions with property-based testing and fast-check

refactoring-property-based.js

const fc = require('fast-check');
const _ = require('lodash');

let selectNames = data => {
  let names = [];
  data.forEach(element => {
    names.push(element.name);
  });
  return names;
};

function refactoredSelectNames(data) {
  return data.map(({ name }) => name);
}

function areEqualFunctions(func1, func2, ...args) {
  return _.isEqual(func1(...args), func2(...args));
}

describe('selectNames', () => {
  test('both functions are equal', () => {
    const areEqualFunctionsProperty = _.partial(
      areEqualFunctions,
      selectNames,
      refactoredSelectNames
    );

    const domain = fc.array(fc.record({ name: fc.anything() }));

    fc.assert(fc.property(domain, areEqualFunctionsProperty), { verbose: true });
  });
});