Add test for LowPassFilter

Summary: Eating my own dogfood.

Reviewed By: mweststrate

Differential Revision: D21545655

fbshipit-source-id: 1e2690478ad8a986915a98a8275a168fa4c3a23f

desktop/app/src/utils/__tests__/LowPassFilter.node.tsx

@@ -0,0 +1,46 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import LowPassFilter from '../LowPassFilter';
+
+test('hasFullBuffer', () => {
+  const lpf = new LowPassFilter();
+  expect(lpf.hasFullBuffer()).toBeFalsy();
+
+  lpf.push(1);
+  lpf.push(2);
+  lpf.push(3);
+  lpf.push(4);
+  lpf.push(5);
+
+  expect(lpf.hasFullBuffer()).toBeTruthy();
+});
+
+test('push on full buffer returns shifted value', () => {
+  const lpf = new LowPassFilter();
+  expect(lpf.push(1)).toBe(0);
+  expect(lpf.push(2)).toBe(0);
+  expect(lpf.push(3)).toBe(0);
+  expect(lpf.push(4)).toBe(0);
+  expect(lpf.push(5)).toBe(0);
+  expect(lpf.push(6)).toBe(1);
+  expect(lpf.push(7)).toBe(2);
+});
+
+test('next returns smoothed value', () => {
+  const lpf = new LowPassFilter();
+  expect(lpf.next(1)).toBe(0.9);
+  expect(lpf.next(2)).toBe(1.881);
+});
+
+test('next returns smoothed value with custom smoothing', () => {
+  const lpf = new LowPassFilter(0.5);
+  expect(lpf.next(1)).toBe(0.5);
+  expect(lpf.next(2)).toBe(1.125);
+});