1  import * as assert from 'assert';
 2  import * as fc from 'fast-check';
 3  import { stableSort } from './implem';
 4  
 5  const count = (tab, element) => tab.filter(v => v === element).length;
 6  
 7  describe('stable sort', () => {
 8    it('should contain the same items', () =>
 9      fc.assert(
10        fc.property(fc.array(fc.integer()), data => {
11          const sorted = stableSort(data.slice(0), (a, b) => a - b);
12          assert.equal(sorted.length, data.length);
13          for (const item of data) assert.equal(count(sorted, item), count(data, item));
14        })
15      ));
16    it('should produce ordered array', () =>
17      fc.assert(
18        fc.property(fc.array(fc.integer()), data => {
19          const sorted = stableSort(data, (a, b) => a - b);
20          for (let idx = 1; idx < sorted.length; ++idx) assert.ok(sorted[idx - 1] <= sorted[idx]);
21        })
22      ));
23    it('should be stable', () =>
24      fc.assert(
25        fc.property(fc.array(fc.record({ key1: fc.nat(5), key2: fc.nat(5) })), data => {
26          const singleSort = stableSort(data, (a, b) => {
27            if (a.key2 < b.key2) return -1;
28            else if (a.key2 > b.key2) return 1;
29            return a.key1 - b.key1;
30          });
31          const sorted = stableSort(stableSort(data, (a, b) => a.key1 - b.key1), (a, b) => a.key2 - b.key2);
32          assert.deepStrictEqual(sorted, singleSort);
33        })
34      ));
35  });