* Rename test directory to spec

* Install rspec gem

* Rename test files to spec files

* Rewrite Command specs

* Rewrite Compiler specs

* Rewrite CompilerStrategy specs

* Rewrite Configuration specs

* Rewrite DevServerRunner specs

* Rewrite DevServer specs

* Rewrite DigestStrategy specs

* Rewrite EngineRakeTasks specs

* Rewrite Env specs

* Rewrite Webpacker::Helper specs

* Rewrite Webpacker::Manifest specs

* Rewrite Webpacker::MtimeStrategy specs

* Rewrite RakeTasks specs

* Rewrite VersionChecker specs

* Rewrite WebpackRunner specs

* Rewrite Webpacker specs

* Use mock for dev_server

* Refactor Configuration specs

* Improve doubles

* Improve doubles

* Improve spec title

* Improve code organization

Improve tests

* Use verifying double

* Reorganize the code

* Remove redundant spec

This spec is already tested more robustly in the following dedicated files:
- env_spec.erb
- configuration_spec.rb

* Use each instead of example in before hook