test(shared): tweak isLinkExternal test cases

Author: meteorlxy

packages/@vuepress/shared/__tests__/utils/isLinkExternal.spec.ts

@@ -4,16 +4,22 @@ const testCases: [
   Parameters<typeof isLinkExternal>,
   ReturnType<typeof isLinkExternal>
 ][] = [
+  // with default base `/`
   [['https://foobar.com'], true],
   [['http://foobar.com'], true],
   [['//foobar.com'], true],
   [['foobar.com'], false],
   [['/foo/bar'], false],
+  [['foo/bar'], false],
+  [['../foo/bar'], false],
+
+  // with base `/base/`
   [['/foo/bar', '/base/'], true],
+  [['foo/bar', '/base/'], false],
+  [['../foo/bar', '/base/'], false],
   [['/base/foo/bar', '/base/'], false],
   [['mailto:foobar', '/base/'], false],
   [['tel:foobar', '/base/'], false],
-  [['../foo/bar', '/base/'], false],
 ]
 
 describe('shared > isLinkExternal', () => {