calc

#! /usr/bin/env node

const Calculator = require('./Calculator')

const calculator = new Calculator()
const [a, b] = process.argv.slice(2)
console.log(calculator.add(Number(a), Number(b)))

calculator.js

module.exports = class Calculator {
  add (a, b) {
    return a + b
  }
}

CommandLineSetup.js

const child_process = require('child_process')
const {promisify} = require('util')
const exec = promisify(child_process.exec)

module.exports = class CommandLineSetup {
  setup () {
  }

  teardown () {
  }

  user () {
    return {
      assertAddCalculation: async (a, b, result) => {
        const actualResult = Number((await exec(__dirname + `/calc ${a} ${b}`)).stdout.trim())
        if (result !== actualResult) {
          throw new Error(`expected calculator result ${result} but was ${actualResult}`)
        }
      }
    }
  }
}

CoreSetup.js

const Calculator = require('./Calculator')

module.exports = class CoreSetup {
  setup () {
    this.calculator = new Calculator()
  }

  teardown () {
    delete this.calculator
  }

  user () {
    return {
      assertAddCalculation: async (a, b, result) => {
        const actualResult = this.calculator.add(a, b)
        if (result !== actualResult) {
          throw new Error(`expected calculator result ${result} but was ${actualResult}`)
        }
      }
    }
  }
}

describeFeature.js

const setups = [
  require('./CommandLineSetup'),
  require('./CoreSetup'),
  require('./HttpApiSetup')
]

module.exports = function describeFeature(name, definition) {
  describe(name, () => {
    setups.forEach(Setup => {
      describe(Setup.name, () => {
        definition(Setup)
      })
    })
  })
}

httpApi.js

const Calculator = require('./Calculator')
const express = require('express')

const app = express()

app.get('/add', (req, res) => {
  const {a, b} = req.query
  const calculator = new Calculator()
  const result = calculator.add(Number(a), Number(b))
  res.json(result)
})

module.exports = app

HttpApiSetup.js

const httpApi = require('./httpApi')
const httpism = require('httpism')
const {promisify} = require('util')

module.exports = class HttpApiSetup {
  async setup () {
    const listen = promisify((...args) => this.server = httpApi.listen(...args))
    await listen(4567)
  }

  async teardown () {
    const close = promisify(this.server.close).bind(this.server)
    await close()
    delete this.server
  }

  user () {
    return {
      assertAddCalculation: async (a, b, result) => {
        const actualResult = await httpism.get(`http://localhost:4567/add`, {params: {a, b}})
        if (result !== actualResult) {
          throw new Error(`expected calculator result ${result} but was ${actualResult}`)
        }
      }
    }
  }
}

output

  adding numbers
    CommandLineSetup
      ✓ can add two numbers (91ms)
      ✓ can add a positive and negative number (90ms)
    CoreSetup
      ✓ can add two numbers
      ✓ can add a positive and negative number
    HttpApiSetup
      ✓ can add two numbers
      ✓ can add a positive and negative number


  6 passing (225ms)

test.js

const describeFeature = require('./describeFeature')

describeFeature('adding numbers', Setup => {
  let user

  beforeEach(async () => {
    setup = new Setup()
    await setup.setup()
    user = setup.user()
  })

  afterEach(async () => {
    await setup.teardown()
  })

  it('can add two numbers', async () => {
    await user.assertAddCalculation(1, 2, 3)
  })

  it('can add a positive and negative number', async () => {
    await user.assertAddCalculation(1, -2, -1)
  })
})