Testing with generator functions

handler.js

const action = (name, ...args) => {
  return [name, args];
};

const GET_TODOS = Symbol.for('action.getTodos');

const getTodos = action.bind(null, GET_TODOS);

function* route() {
  let todos = yield getTodos();
  
  return {
    isBase64Encoded: false,
    statusCode: 200,
    headers: {
      'content-type': 'application/json'
    },
    body: JSON.stringify(todos)
  };
}


async function run(gen, context) {
  let defaultPerformAction = () => {};
  let result = gen.next(value);
  
  while(!result.done) {
    let [action, args] = result.value;
    let performAction = context[action] || defaultPerformAction;
    let value = performAction(...args);
    
    if(value.then) {
      value = await value;
    }
    
    result = gen.next(value);
  }
  
  return result.value;
}

exports.run = run;
exports.route = route;
exports.handler = async function(e) {
  let gen = route();
  
  return run(gen, {
    [GET_TODOS]() { return db.scan({ TableName: 'todos' }) }
  });
};

test.js

const assert = require('assert');
const { route, run } = require('./handler.js');

describe('Todos', () => {
  it('gets the todos', async () => {
    let result = await run(route(), {
      [Symbol.for('action.getTodos')]() {
        return [{label: 'walk the dog'}, {label: 'pick up dry cleaning'}];
      }
    });
    
    let data = JSON.parse(result.body);
    
    assert.equal(data.length, 2);
    assert.equal(data[0].label, 'walk the dog');
  });
});