Added optimization test

tests/react.spec.tsx

@@ -1,8 +1,14 @@
-import { val } from 'rval'
+import { val, drv } from 'rval'
 import { useVal } from 'rval/react'
 import * as React from 'react'
 import { render, waitForElement } from 'react-testing-library'
 
+function delay(time) {
+  return new Promise(resolve => {
+    setTimeout(resolve, time)
+  })
+}
+
 test('useVal - 1 ', async () => {
   const counter = val(0)
   const Comp = () => {
@@ -19,3 +25,49 @@ test('useVal - 1 ', async () => {
   counter(counter() + 1)
   await waitForElement(() => re.container.innerHTML === '<h1>2</h1>')
 })
+
+test('useVal - mimimum computations - 1', async () => {
+  const counter = val(0)
+  let called = 0
+  const doubler = drv(() => {
+    called++
+    return counter() * 2
+  })
+
+  const Comp = () => {
+    const c = useVal(doubler)
+    return <h1>{c}</h1>
+  }
+
+  const re = render(<Comp />)
+  expect(re.container.innerHTML).toEqual('<h1>0</h1>')
+  expect(called).toBe(1)
+
+  counter(counter() + 1)
+  await waitForElement(() => re.container.innerHTML === '<h1>2</h1>')
+  expect(called).toBe(2)
+
+  counter(counter() + 1)
+  await waitForElement(() => re.container.innerHTML === '<h1>4</h1>')
+  expect(called).toBe(3)
+})
+
+test('useVal - mimimum computations - 1', async () => {
+  const counter = val(0)
+  let called = 0
+  const doubler = drv(() => {
+    called++
+    return counter() * 2
+  })
+
+  const Comp = () => {
+    const c = useVal(doubler)
+    return <h1>{c}</h1>
+  }
+
+  const re = render(<Comp />)
+  expect(re.container.innerHTML).toEqual('<h1>0</h1>')
+
+  await delay(100)
+  expect(called).toBe(1) // and not 2!
+})