Fix the generator tests

Author: alexeyr

CONTRIBUTING.md

@@ -216,7 +216,7 @@ yalc add react-on-rails
 ### Testing the Generator
 The generators are covered by generator tests using Rails's generator testing helpers, but it never hurts to do a sanity check and explore the API. See [generator_testing_script.md](generator_testing_script.md) for a script on how to run the generator on a fresh project.
 
-`rake run_rspec:example_basic` is a great way to run tests on one generator. Once that works, you should run `rake run_rspec:examples`. Be aware that this will create a hug number of files under a `/gen-examples` directory. You should be sure to exclude this directory from your IDE and delete it once your testing is done.
+`rake run_rspec:shakapacker_examples_basic` is a great way to run tests on one generator. Once that works, you should run `rake run_rspec:shakapacker_examples`. Be aware that this will create a huge number of files under a `/gen-examples` directory. You should be sure to exclude this directory from your IDE and delete it once your testing is done.
 
 ### Linting
 All linting is performed from the docker container for CI. You will need docker and docker-compose installed locally to lint code changes via the lint container. You can lint locally by running `npm run lint && npm run flow`

lib/generators/react_on_rails/dev_tests_generator.rb

@@ -47,14 +47,10 @@ def replace_prerender_if_server_rendering
 
       def add_yarn_relative_install_script_in_package_json
         package_json = File.join(destination_root, "package.json")
-        contents = File.read(package_json)
-        replacement_value = <<-STRING
-  "scripts": {
-    "postinstall": "yalc link react-on-rails",
-        STRING
-        new_client_package_json_contents = contents.gsub(/ {2}"scripts": {/,
-                                                         replacement_value)
-        File.open(package_json, "w+") { |f| f.puts new_client_package_json_contents }
+        contents = JSON.parse(File.read(package_json))
+        contents["scripts"] ||= {}
+        contents["scripts"]["postinstall"] = "yalc link react-on-rails"
+        File.open(package_json, "w+") { |f| f.puts JSON.pretty_generate(contents) }
       end
     end
   end