refactor: improve error message

Author: eddyerburgh

packages/create-instance/extend-extended-components.js

@@ -65,12 +65,16 @@ export function extendExtendedComponents (
     if (shouldExtendComponent) {
       if (logModifiedComponents) {
         warn(
-          `an extended child component <${c}> has been modified ` +
-          `to ensure it has the correct instance properties. ` +
-          `This means it is not possible to find the component ` +
-          `with a component selector. To find the component, ` +
-          `you must stub it manually using the stubs mounting ` +
-          `option.`
+          `The child component <${c}> has been modified to ensure ` +
+          `it is created with properties injected by Vue Test Utils. \n` +
+          `This is because the component was created with Vue.extend, ` +
+          `or uses the Vue Class Component decorator. \n` +
+          `Because the component has been modified, it is not possible ` +
+          `to find it with a component selector. To find the ` +
+          `component, you must stub it manually using the stubs mounting ` +
+          `option, or use a name or ref selector. \n` +
+          `You can hide this warning by setting the Vue Test Utils ` +
+          `config.logModifiedComponents option to false.`
         )
       }
       extendedComponents[c] = _Vue.extend(comp)

test/specs/mount.spec.js

@@ -164,11 +164,16 @@ describeRunIf(process.env.TEST_ENV !== 'node', 'mount', () => {
 
   it('logs if component is extended', () => {
     const msg =
-      `[vue-test-utils]: an extended child component <ChildComponent> ` +
-      `has been modified to ensure it has the correct instance properties. ` +
-      `This means it is not possible to find the component with a component ` +
-      `selector. To find the component, you must stub it manually using the ` +
-      `stubs mounting option.`
+      `[vue-test-utils]: The child component <ChildComponent> has been modified to ensure ` +
+      `it is created with properties injected by Vue Test Utils. \n` +
+      `This is because the component was created with Vue.extend, ` +
+      `or uses the Vue Class Component decorator. \n` +
+      `Because the component has been modified, it is not possible ` +
+      `to find it with a component selector. To find the ` +
+      `component, you must stub it manually using the stubs mounting ` +
+      `option, or use a name or ref selector. \n` +
+      `You can hide this warning by setting the Vue Test Utils ` +
+      `config.logModifiedComponents option to false.`
     const ChildComponent = Vue.extend({
       template: '<span />'
     })