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breadboard

Breadboard

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Breadboard is an opinionated inversion of control container for Node.js applications.

Motivation

  • Working with require is less than ideal.
    • The same module will have a different key depending on the path of the requiring module.
    • Testing a module in isolation, ie. mocking its dependencies, requires hacky solutions that hijack require calls. This approach is indeterministic, depending on various seemingly unrelated conditions around how the the module you want to mock was defined.
  • Discouraging managing state of the app through side effects when requireing.
  • Single function call to auto-mock a module's dependencies in your tests.

Breadboard will lazily require all your application's dependencies defined in package.json, all Node native modules and all of your application's modules and store them in a dependencies object. The object is exposed to your application's modules by calling the modules as functions, passing the dependencies as an argument. As such, your modules are expected to be wrapped in an extra function returning the desired export value, which Breadboard then calls on application start.

Install

npm install breadboard

Example of a module in your application

Consider this CommonJS module:

//startServer.js 
 
const d = require('debug')('myApp');
const createServer = require('./lib/createServer');
 
module.exports = () => {
  const server = createServer();
 
  server.listen(80, () => {
    d('Server listening on port 80');
  });
 
  return server;
};

The Breadboard equivalent would be:

//startServer.js 
 
// wrap module in factory function 
module.exports = ({ // destructure dependencies to get the modules needed 
    debug,
    '/lib/createServer': createServer
  }) => {
  // return the core functionality of the module as a function 
  return () => {
    const server = createServer();
    const d = debug('myApp');
 
    server.listen(80, () => {
      d('Server listening on port 80');
    });
 
    return server;
  };
};

To start your application:

 
const breadboard = require('breadboard');
 
breadboard({
  entry: '/index',
  containerRoot: 'app',
  initialState: {
    arbitrary: 'state data'
  },
  blacklist: ['newrelic']
}).then(({deps, entryResolveValue}) => {
  console.log('Application started', deps, entryResolveValue);
});

Further examples

Take a look at examples/kitchen. To run, npm install then npm start.

Module keys

Module keys in a Breadboard app are static, ie. are always relative to the container's root folder, starting with /, and always using / as path separators, no matter the platform. Consider these example module keys:

/lib/getUser
/middleware/getUser
/logger

Keys for native Node.js modules and 3rd party modules remain the same as if you were using require. Breadboard also loads all JSON files. To access them, append .json to the end of the key, eg. /data/userPasswords.json.

API

breadboard(options)

Returns a promise chained to the return value of your application's entry point, which might be another promise or a concrete value. ### options #### options.entry (String | Function<Object>) ##### String Module key for the entry point of the application. ##### Function<Object> Will be called as the entry point module, with resolved dependencies as the argument. #### options.containerRoot (String) Path relative to the current working directory, from which all module keys will be resolved #### options.initialState (Object) The argument the entry function will be called with. #### options.blacklist (Array<String>) List of modules from your package.json which you wish Breadboard not to load. If you want to defer a require call to a 3rd party module, put it in the blacklist and require manually in your code. #### options.substitutes (Object) A Breadboard module-key to module mapping to indicate which modules you want to substitute across the whole application with your custom implementation. Useful when testing integration of multiple modules. You could substitute eg. a database connector with a stub to remove a running database as a dependency of your tests.

Testing

In tests require your Breadboard modules as if they were CommonJS modules. You can then supply your own stubs and spies as test doubles. Consider the following example: ### Test subject module /index

module.exports = (deps) => {
  return () => {
    const {
      '/widgets/createDough': createDough,
      '/pasta/createPapardelle': createPapardelle,
      'debug': debug 
    } = deps;
    const d = debug('pasta');
 
    d(createPapardelle(createDough()));
  };
};

Test for /index

import { expect } from 'chai';
import mainFactory from '../../app/index';
import sinon from 'sinon';
 
describe('Main', () => {
  const sandbox = sinon.sandbox.create();
  const debugSpy = sandbox.spy();
  const mockDough = 'dough';
  const mockDependencies = {
    debug: sandbox.stub().returns(debugSpy),
    '/widgets/createDough': sandbox.stub().returns(mockDough),
    '/pasta/createPapardelle': sandbox.spy()
  };
  let main;
 
  beforeEach(() => {
    main = mainFactory(mockDependencies);
  });
  afterEach(() => {
    sandbox.reset();
  });
  it('calls debug', () => {
    main();
    expect(mockDependencies.debug.calledOnce).to.be.true;
  });
  it('calls createDough', () => {
    main();
    expect(mockDependencies['/widgets/createDough'].calledOnce).to.be.true;
  });
  it('calls createPapardelle with createDough return value', () => {
    main();
    expect(mockDependencies['/pasta/createPapardelle'].calledWith(mockDough)).to.be.true;
  });
});

autoMock

autoMock automatically replaces every dependency of a given Breadboard module with a Sinon.JS stub.

autoMock API

autoMock(factory, options) #### factory (Function) The Breadboard factory function to build the subject to test. #### options (Object) ##### options.mocks (Object) A Breadboard module-key to module mapping to indicate which modules you want to mock manually. #### returns Object<subject, deps, sandbox> ##### subject The module returned by factory. ##### deps The mock dependencies injected into subject. ##### sandbox Instance of a Sinon.JS sandbox.

autoMock example

Test subject module /index

module.exports = (deps) => {
  return function main() {
    const {
      '/widgets/createDough': createDough,
      '/pasta/createPapardelle': createPapardelle,
      'debug': debug 
    } = deps;
    const d = debug('pasta');
 
    d(createPapardelle(createDough()));
  };
};

Test for module /index

import { expect } from 'chai';
import mainFactory from '../../app/index';
import autoMock from 'breadboard/lib/autoMock';
 
const mockDough = 'dough';
const {subject: main, sandbox, deps} = autoMock(mainFactory);
const debugSpy = sandbox.spy();
 
deps.debug.returns(debugSpy);
deps['/widgets/createDough'].returns(mockDough);
describe('Main', () => {
  afterEach(() => {
    sandbox.reset();
  });
  it('calls debug', () => {
    main();
    expect(deps.debug.calledOnce).to.be.true;
  });
  it('calls createDough', () => {
    main();
    expect(deps['/widgets/createDough'].calledOnce).to.be.true;
  });
  it('calls createPapardelle with createDough return value', () => {
    main();
    expect(deps['/pasta/createPapardelle'].calledWith(mockDough)).to.be.true;
  });
});