test: add IntroSort tests

Author: crhallberg

Sorts/test/IntroSort.test.js

@@ -0,0 +1,73 @@
+import { introsort } from '../IntroSort'
+
+describe('introsort', () => {
+  it('should have a robust default comparator', () => {
+    // toString, null, undefined
+    const mixedData = [undefined, '2', 1, false, null]
+    introsort(mixedData)
+    expect(mixedData).toEqual([1, '2', false, null, undefined])
+
+    // Symbol
+    expect(() => introsort([Symbol(), Symbol()])).toThrowError()
+  })
+
+  it('fails gracefully', () => {
+    introsort('string')
+    introsort([])
+    introsort([1, 2, 3], 'string')
+  })
+
+  it('should sort randomly generated data', function demo1() {
+    // make array
+    const data = []
+    const size = 10_000
+    for (let i = 0; i < size; i++) {
+      const temp = Math.random() * Number.MAX_SAFE_INTEGER
+      data.push(temp)
+    }
+
+    // custom comparator
+    const c = function (a, b) {
+      return a - b
+    }
+    introsort(data, c)
+
+    // check that all numbers are smaller than the one after them
+    let faulty = false
+    for (let i = 1; i < size; i++) {
+      if (data[i - 1] > data[i]) {
+        faulty = true
+        break
+      }
+    }
+
+    expect(faulty).toEqual(false)
+  })
+
+  it('should match the sorting of Array.sort()', function demo2() {
+    // make arrays
+    const data = []
+    const data2 = []
+    const size = 10_000
+    for (let i = 0; i < size; i++) {
+      const temp = Math.random() * Number.MAX_SAFE_INTEGER
+      data.push(temp)
+      data2.push(temp)
+    }
+
+    // sort
+    introsort(data)
+    data2.sort()
+
+    // verify
+    let faulty = false
+    for (let i = 0; i < size; i++) {
+      if (data[i] !== data2[i]) {
+        faulty = true
+        break
+      }
+    }
+
+    expect(faulty).toEqual(false)
+  })
+})