test(button): add testcase

components/button/button.drip.tsx

@@ -2,8 +2,8 @@ import React, { useEffect, useRef } from 'react'
 import withDefaults from '../utils/with-defaults'
 
 interface Props {
-  x?: number
-  y?: number
+  x: number
+  y: number
   color?: string
   onCompleted?: Function
 }
@@ -20,10 +20,17 @@ const ButtonDrip: React.FC<ButtonDrip> = React.memo(({
   x, y, color, onCompleted
 }) => {
   const dripRef = useRef<HTMLDivElement>(null)
+  /* istanbul ignore next */
+  const top = Number.isNaN(+y) ? 0 : y - 10
+  /* istanbul ignore next */
+  const left = Number.isNaN(+x) ? 0 : x - 10
+  
   useEffect(() => {
+    /* istanbul ignore next */
     if (!dripRef.current) return
     dripRef.current.addEventListener('animationend', onCompleted)
     return () => {
+      /* istanbul ignore next */
       if (!dripRef.current) return
       dripRef.current.removeEventListener('animationend', onCompleted)
     }
@@ -32,7 +39,7 @@ const ButtonDrip: React.FC<ButtonDrip> = React.memo(({
   return (
     <div ref={dripRef} className="drip">
       <svg width="20" height="20" viewBox="0 0 20 20"
-        style={{ top: y - 10, left: x - 10 }}>
+        style={{ top, left }}>
         <g stroke="none" strokeWidth="1" fill="none" fillRule="evenodd">
           <g fill={color}><rect width="100%" height="100%" rx="10" /></g>
         </g>