abovefoldAlgorithm: add basic tests

app/soapbox/features/timeline-insertion/__tests__/abovefold.test.ts

@@ -0,0 +1,18 @@
+import { abovefoldAlgorithm } from '../abovefold';
+
+const DATA = Object.freeze(['a', 'b', 'c', 'd']);
+
+test('abovefoldAlgorithm', () => {
+  const result = Array(50).fill('').map((_, i) => {
+    return abovefoldAlgorithm(DATA, i, { seed: '!', range: [2, 6], pageSize: 20 });
+  });
+
+  // console.log(result);
+  expect(result[0]).toBe(undefined);
+  expect(result[4]).toBe('a');
+  expect(result[5]).toBe(undefined);
+  expect(result[24]).toBe('b');
+  expect(result[30]).toBe(undefined);
+  expect(result[42]).toBe('c');
+  expect(result[43]).toBe(undefined);
+});

app/soapbox/features/timeline-insertion/types.ts

@@ -3,7 +3,7 @@
  */
 type PickAlgorithm = <D = any>(
   /** Elligible candidates to pick. */
-  items: D[],
+  items: readonly D[],
   /** Current iteration by which an item may be chosen. */
   iteration: number,
   /** Implementation-specific opts. */