improve coverage

Author: yyx990803

src/index.js

@@ -250,6 +250,7 @@ class Router {
           'root container.'
         )
       }
+      /* istanbul ignore if */
       if (App instanceof Vue) {
         throw new Error(
           'Must start vue-router with a component, not a ' +

src/util.js

@@ -15,7 +15,6 @@ export function warn (msg) {
   /* istanbul ignore next */
   if (window.console) {
     console.warn('[vue-router] ' + msg)
-    /* istanbul ignore if */
     if (!exports.Vue || exports.Vue.config.debug) {
       console.warn(new Error('warning stack trace:').stack)
     }
@@ -137,6 +136,7 @@ export function resolveAsyncComponent (handler, cb) {
 export function mapParams (path, params = {}, query) {
   path = path.replace(/:([^\/]+)/g, (_, key) => {
     let val = params[key]
+    /* istanbul ignore if */
     if (!val) {
       warn(
         'param "' + key + '" not found when generating ' +

test/unit/specs/core.js

@@ -342,7 +342,7 @@ describe('Core', function () {
     router.start({
       replace: false,
       template:
-        '<div v-link><a id="link" href="/a"></a></div>' +
+        '<div v-link><a href="/a"><span id="link"></span></a></div>' +
         '<router-view></router-view>'
     }, el)
     var link = el.querySelector('#link')