fix(@angular-devkit/build-angular): add a base href to karma context (#12889)

cexbrayat · vikerman · commit f3b8557d4ee2 · 2018-11-08T10:56:20.000-08:00
This commits adds a base href value in the karma context iframe used to run unit tests. It solves a very old issue in Angular angular/angular#12295 where a unit test throws: No base href set. Please provide a value for the APP_BASE_HREF token or add a base element to the document. even if the application is fine. This is because the `index.html` from Angular CLI contains a base href value, but not the Karma context iframe. So when adding a unit test with a testing module that imports a NgModule, for example `AppModule`, which itself imports `RouterModule`, the unit test used to throw an error (regression appeared in router 3.1). That could be solved by either adding `RouterTestingModule` to the testing module, or by adding a provider `{ provide: APP_BASE_HREF, useValue: '/' }`, but required to understand the issue (see how many thumbs up there are on the original issue). This solves the issue in a transparent way: developers won't even encounter the problem anymore.
diff --git a/packages/angular_devkit/build_angular/src/angular-cli-files/plugins/karma-context.html b/packages/angular_devkit/build_angular/src/angular-cli-files/plugins/karma-context.html
@@ -8,6 +8,7 @@
 
 <head>
   <title></title>
+  <base href="/">
   <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
   <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no" />
 </head>
