There are a two seemingly-similar complaints when first getting started with Karma:
[preprocess]: Can not load "webpack", it is not registered!
Perhaps you are missing some plugin?
and
[plugin]: Cannot find plugin "karma-webpack".
Did you forget to install it ?
npm install karma-webpack --save-dev
The following is my best recommendation for fixing these two problems with your configuration…
“Can not load “XYZ”, it is not registered!” (sic)
The typical solution to the ‘Perhaps you are missing some plugin?’ message is to make sure it’s included within the plugins array in karma.conf.js.
plugins: [
'karma-chrome-launcher',
'karma-tap',
'karma-sourcemap-loader',
'karma-webpack' // *** This 'registers' the Karma webpack plugin.
],
“Cannot find plugin ‘karma-xyz’.”
If you’ve already installed it by running npm install karma-xyz --save-dev, but Karma still prompts (read: taunts) you with the “Did you forget to install it ?” warning, you may have a global installation of the Karma module.
Chances are that when you installed a global copy of the karma-cli using -g, you included karma (or were told to do so by a well-meaning tutorial), but that can cause problems resolving modules in certain versions (i.e., every version I’ve ever used). Karma’s installation documentation recommends that the module should be a local installation using npm install karma --save-dev.
If you have a global Karma installation, try something like:
$ npm uninstall -g karma
$ npm install karma --save-dev