test.js

'use strict'

const test = require('tap').test
const Histogram = require('./')

test('create an histogram', (t) => {
  t.doesNotThrow(() => Histogram(1, 100))
  t.end()
})

test('create an histogram with a constructor', (t) => {
  t.doesNotThrow(() => new Histogram(1, 100))
  t.end()
})

test('create an histogram arguments checks', (t) => {
  t.throws(() => Histogram(-1, 100))
  t.throws(() => Histogram(0, 100))
  t.throws(() => Histogram(1, 100, 20))
  t.throws(() => Histogram(1, 100, 0))
  t.throws(() => Histogram(1, 100, 6))
  for (let i = 1; i < 5; i++) {
    t.doesNotThrow(() => Histogram(1, 100, i))
  }
  t.end()
})

test('record values in an histogram', (t) => {
  const instance = new Histogram(1, 100)
  t.ok(instance.record(42))
  t.ok(instance.record(45))
  t.end()
})

test('recording a non-value returns false', (t) => {
  const instance = Histogram(1, 100)
  t.notOk(instance.record())
  t.notOk(instance.record(-42))
  t.end()
})

test('stdev, mean, min, max', (t) => {
  const instance = Histogram(1, 100)
  t.ok(instance.record(42))
  t.ok(instance.record(45))
  t.equal(instance.min(), 42, 'min is available')
  t.equal(instance.max(), 45, 'max is available')
  t.equal(instance.mean(), 43.5, 'mean is available')
  t.equal(instance.stddev(), 1.5, 'stdev is available')
  t.end()
})

test('percentile', (t) => {
  const instance = Histogram(1, 100)
  t.ok(instance.record(42))
  t.ok(instance.record(42))
  t.ok(instance.record(45))
  t.equal(instance.percentile(10), 42, 'percentile match')
  t.equal(instance.percentile(99), 45, 'percentile match')
  t.equal(instance.percentile(100), 45, 'percentile match')
  t.end()
})

test('wrong percentile', (t) => {
  const instance = Histogram(1, 100)
  t.ok(instance.record(42))
  t.ok(instance.record(42))
  t.ok(instance.record(45))
  t.throws(() => instance.percentile(), 'no percentile throws')
  t.throws(() => instance.percentile(101), 'percentile > 100 throws')
  t.throws(() => instance.percentile(0), 'percentile == 0 throws')
  t.throws(() => instance.percentile(-1), 'percentile < 0 throws')
  t.end()
})

test('encode/decode', (t) => {
  const instance = Histogram(1, 100)
  t.ok(instance.record(42))
  t.ok(instance.record(42))
  t.ok(instance.record(45))
  const instance2 = Histogram.decode(instance.encode())
  t.equal(instance2.percentile(10), 42, 'percentile match')
  t.equal(instance2.percentile(99), 45, 'percentile match')
  t.end()
})

test('fail decode', (t) => {
  t.throws(() => Histogram.decode())
  t.throws(() => Histogram.decode('hello'))
  t.throws(() => Histogram.decode({}))
  t.throws(() => Histogram.decode(42))
  t.end()
})

test('percentiles', (t) => {
  const instance = Histogram(1, 100)
  t.deepEqual(instance.percentiles(), [{
    percentile: 100,
    value: 0
  }], 'empty percentiles has 0 till 100%')
  t.ok(instance.record(42))
  t.ok(instance.record(42))
  t.ok(instance.record(45))
  t.deepEqual(instance.percentiles(), [{
    percentile: 0,
    value: 42
  }, {
    percentile: 50,
    value: 42
  }, {
    percentile: 75,
    value: 45
  }, {
    percentile: 100,
    value: 45
  }], 'percentiles matches')
  t.end()
})