Implement basic dice

2 files changed, 137 insertions, 0 deletions

diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
new file mode 100644
index 0000000..9df156f
--- /dev/null
+++ b/__tests__/dice.test.js
@@ -0,0 +1,119 @@
+const { d } = require('../src/dice.js')
+
+const defaultNumberRolls = 100
+
+expect.extend({
+  toBeOnAverage(received, expected, margin = 0.3) {
+    const average = received.reduce(plus) / received.length
+    const pass = average > expected - margin && average < expected + margin
+
+    return {
+      pass,
+      message: () => (
+        `expected average to${pass ? ' not ' : ' '}be around ${expected} (margin: ${margin}), got ${average}`
+      )
+    }
+  },
+  toBeBetween(received, low, high) {
+    const pass = received.reduce((allOk, value) => {
+      return allOk && value >= low && value <= high
+    }, true)
+
+    return {
+      pass,
+      message: () => (
+        `expected all to${pass ? ' not ' : ' '}be between ${low} and ${high}`
+      )
+    }
+  },
+  toAllBe(received, expected) {
+    const pass = received.reduce((allOk, value) => {
+      return allOk && value === expected
+    })
+
+    return {
+      pass,
+      message: () => (
+        `expected all to${pass ? ' not ' : ' '}be equal to ${expected}`
+      )
+    }
+  }
+})
+
+const plus = (a, b) => (a + b)
+
+const rollForTest = (die, numberRolls) => {
+  let pools = []
+  let rolls = []
+
+  for (let i = 0; i < numberRolls; i++) {
+    let rolled = die()
+    pools.push(rolled)
+    rolls.push(rolled.reduce(plus))
+  }
+
+  return { pools, rolls }
+}
+
+const testDie = (die, numberRolls, testSpecs) => {
+  let { pools, rolls } = rollForTest(die, numberRolls)
+
+  if ('diceCount' in testSpecs) {
+    it(`rolls ${testSpecs.diceCount} dice`, () => {
+      expect(pools.map((pool) => (pool.length))).toAllBe(testSpecs.diceCount)
+    })
+  }
+
+  if ('average' in testSpecs) {
+    let { average, margin } = testSpecs.average
+
+    it(`has an expected value of ${average}`, () => {
+      expect(rolls).toBeOnAverage(average, margin)
+    })
+  }
+
+  if ('bounds' in testSpecs) {
+    let { low, high } = testSpecs.bounds
+
+    it(`rolls between ${low} and ${high}`, () => {
+      expect(rolls).toBeBetween(low, high)
+    })
+
+    it('attains its minimum', () => {
+      expect(rolls).toContain(low)
+    })
+
+    it('attains its maximum', () => {
+      expect(rolls).toContain(high)
+    })
+  }
+}
+
+const describeBasicDie = (number, sides, numberRolls = defaultNumberRolls) => {
+  describe(`${number}d${sides}`, () => {
+    const die = d(number, sides)
+    const min = number
+    const max = number * sides
+
+    const testSpecs = {
+      diceCount: number,
+      average: {
+        average: (min + max) / 2,
+      },
+      bounds: {
+        low: min,
+        high: max,
+        expectLow: true,
+        expectHigh: true
+      }
+    }
+
+    testDie(die, numberRolls, testSpecs)
+  })
+}
+
+describe('basic dice', () => {
+  describeBasicDie(1, 6)
+  describeBasicDie(2, 8)
+  describeBasicDie(20, 1)
+})
diff --git a/src/dice.js b/src/dice.js
new file mode 100644
index 0000000..2914317
--- /dev/null
+++ b/src/dice.js
@@ -0,0 +1,18 @@
+const d = (number, sides) => {
+  return () => {
+    let pool = []
+
+    for (let i = 0; i < number; i++) {
+      pool.push(1 + Math.floor(Math.random() * sides))
+    }
+
+    return pool
+  }
+}
+
+const roll = (die) => {
+  return die().reduce((a, b) => (a + b))
+}
+
+exports.d = d
+exports.roll = roll