gem install rspec # for rspec-core, rspec-expectations, rspec-mocks
gem install rspec-core # for rspec-core only
rspec-core provides the structure for writing executable examples of how
your code should behave. It uses the words "describe" and "it" so we can
express concepts like a conversation:
"Describe an order."
"It sums the prices of its line
The `rspec` command comes with several options you can use to customize RSpec's
behavior, including output formats, filtering examples, etc.
For a full list of options, run the `rspec` command with the `--help` flag:
$ rspec --help
### Run with `ruby`
Generally, life is simpler if you just use the `rspec` command. If you must use the `ruby`
command, however, you'll want to do the following