docs: add solution for tests in component dir (#1314)

* Add docs for tests in component dir

* Add file path to the example code

Author: ahangarha

README.md

@@ -75,7 +75,7 @@ Read the [full review here](https://clutch.co/profile/shakacode#reviews?sort_by=
   - [Undefined Set](docs/common-errors.md#undefined-set)
   - [Using TheRubyRacer](docs/common-errors.md#using-therubyracer)
   - [HMR](docs/common-errors.md#hmr)
-
+  - [Tests in component directory](docs/common-errors.md#tests-in-component-directory)
 
 After reading this README file, additional information about React-Rails can be found in the Wiki page:
 https://github.com/reactjs/React-Rails/wiki

docs/common-errors.md

@@ -7,6 +7,7 @@
 - [Undefined Set](#undefined-set)
 - [Using TheRubyRacer](#using-therubyracer)
 - [HMR](#hmr)
+- [Tests in component directory](#tests-in-component-directory)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
@@ -45,3 +46,20 @@ LibV8 itself is already [beyond version 7](https://github.com/cowboyd/libv8/rele
 Check out [Enabling Hot Module Replacement (HMR)](https://github.com/shakacode/shakapacker/blob/master/docs/react.md#enabling-hot-module-replacement-hmr) in Shakapacker documentation.
 
 One caveat is that currently you [cannot Server-Side Render along with HMR](https://github.com/reactjs/react-rails/issues/925#issuecomment-415469572).
+
+## Tests in component directory
+
+If your tests for react components reside alongside the component files in the `app/javascript/components` directory,
+you will get `ModuleNotFoundError` in production environment
+since test libraries are devDependencies.
+
+To resolve this issue,
+you need to specify a matching pattern in `appllication.js` and `server_rendering.js`.
+For example, see the below code:
+
+```js
+// app/javascript/packs/application.js
+const componentRequireContext = require.context('react_rails_components', true, /^(?!.*\.test)^\.\/.*$/)
+const ReactRailsUJS = require('react_ujs')
+ReactRailsUJS.useContext(componentRequireContext)
+```