🔍 test(stability): Check that the main sorting method is stable.

Fixes #5.

Author: make-github-pseudonymous-again

test/src/api/stability.js

@@ -0,0 +1,48 @@
+import test from 'ava';
+import {
+	list,
+	all,
+	map,
+	sorted,
+	range,
+	enumerate,
+	nrepeat
+} from '@aureooms/js-itertools';
+import {quasilexicographical, increasing} from '@aureooms/js-compare';
+import {randint} from '@aureooms/js-random';
+
+import sort from '../../../src/array/api/sort';
+
+const isStable = (t, k, M, data) => {
+	t.true(k >= 0);
+	const result = sort(k, M, data.slice());
+	t.true(data.length <= 1 || all(map((tuple) => tuple.length >= k, data)));
+	const lex = quasilexicographical(increasing);
+	const expected = sorted(lex, data);
+	t.deepEqual(expected, result);
+};
+
+const repr = (data) =>
+	data.length >= 20
+		? `[${JSON.stringify(data.slice(0, 9)).slice(1, -1)},..,${JSON.stringify(
+				data.slice(-9)
+		  ).slice(1, -1)}]`
+		: JSON.stringify(data);
+
+isStable.title = (title, k, M, data) =>
+	title || `sort(${k}, ${M}, ${repr(data)}) is stable`;
+
+test(isStable, 0, 0, []);
+test(isStable, 0, 0, list(map((x) => [x], range(1000))));
+test(
+	isStable,
+	1,
+	1,
+	list(map(([a, b]) => [b, a], enumerate(nrepeat(0, 1000))))
+);
+test(
+	isStable,
+	2,
+	2,
+	list(map((i) => [randint(0, 2), randint(0, 2), i], range(1000)))
+);