test: 💍 add tests for useObservable() hook

babel.config.js

@@ -1,3 +1,4 @@
 module.exports = {
     presets: ['@babel/preset-env', '@babel/preset-react', "@babel/preset-typescript"],
+    plugins: ['@babel/plugin-syntax-dynamic-import']
 };

package.json

@@ -44,6 +44,7 @@
   },
   "homepage": "https://github.com/streamich/react-use#readme",
   "dependencies": {
+    "@babel/plugin-syntax-dynamic-import": "^7.2.0",
     "copy-to-clipboard": "^3.1.0",
     "nano-css": "^5.1.0",
     "react-fast-compare": "^2.0.4",

src/__tests__/useObservable.test.tsx

@@ -0,0 +1,35 @@
+import { act, renderHook } from 'react-hooks-testing-library';
+import { Subject } from 'rxjs';
+import { useObservable } from '..';
+
+test('default initial value is undefined', () => {
+  const subject$ = new Subject();
+  const { result } = renderHook(() => useObservable(subject$));
+
+  expect(result.current).toBe(undefined);
+});
+
+test('can specify initial value', () => {
+  const subject$ = new Subject();
+  const { result } = renderHook(() => useObservable(subject$, 123));
+
+  expect(result.current).toBe(123);
+});
+
+test('returns the latest value of observables', () => {
+  const subject$ = new Subject();
+  const { result } = renderHook(() => useObservable(subject$, 123));
+
+  act(() => {
+    subject$.next(125);
+  });
+  expect(result.current).toBe(125);
+
+  act(() => {
+    subject$.next(300);
+    subject$.next(400);
+  });
+  expect(result.current).toBe(400);
+});
+
+xtest('subscribes to observable only once', () => {});