feat(compiler-sfc): warn duplicate block (#451)

packages/compiler-sfc/__tests__/parse.spec.ts

@@ -0,0 +1,21 @@
+import { parse } from '../src'
+import { mockWarn } from '@vue/runtime-test'
+
+describe('compiler:sfc', () => {
+  mockWarn()
+  describe('error', () => {
+    test('should only allow single template element', () => {
+      parse(`<template><div/></template><template><div/></template>`)
+      expect(
+        `Single file component can contain only one template element`
+      ).toHaveBeenWarned()
+    })
+
+    test('should only allow single script element', () => {
+      parse(`<script>console.log(1)</script><script>console.log(1)</script>`)
+      expect(
+        `Single file component can contain only one script element`
+      ).toHaveBeenWarned()
+    })
+  })
+})