Need some help for Software Engineering, on Ruby language.

Overview --------

**You may find the [Ruby documentation at ruby-doc.org](https://ruby-doc.org) helpful to have on hand.**

The repo for this assigment follows a fairly standard Ruby convention for codebases: the code files are stored in `lib/` and the test files are stored in `spec/`. (We use the RSpec unit-testing framework; if we were using Ruby's default framework, known as `Test::Unit`, the test files would be under `test/`.)

We've placed "starter code" in `lib/ruby_intro.rb`; when you're all done, you can submit this single file to the autograder.

However, you can test each of the 3 parts separately. The files `spec/part[123]_spec.rb` contain RSpec tests for each of the three parts. For example, to test your answers to Part 1, say `rspec spec/part1_spec.rb`. `rspec` with no arguments runs the tests in all the files `spec/*_spec.rb`.

* The line numbers in the RSpec error report will give you guidance as to which tests failed. (You can check the [RSpec documentation](http://rspec.info) to see how the `.rspec` file can be used to customize the output format.)

To ensure you have the rspec gem installed you need bundler and can then run bundle install like so:

```sh $ gem install bundler $ cd hw-ruby-intro $ bundle ```

When the above completes successfully you'll have RSpec installed and can run `rspec` from the command line to test your code.

*******************************************************************************ASSIGNMENT*************************************************************************** # 1. Arrays, Hashes, and Enumerables

Check the [Ruby 2.x documentation](http://ruby-doc.org) on `Array`, `Hash` and `Enumerable` as they could help tremendously with these exercises. :-)

0. Define a method `sum(array)` that takes an array of integers as an argument and returns the sum of its elements. For an empty array it should return zero. Run associated tests via: `$ rspec spec/part1_spec.rb:5`

0. Define a method `max_2_sum(array)` which takes an array of integers as an argument and returns the sum of its two largest elements. For an empty array it should return zero. For an array with just one element, it should return that element. Run associated tests via: `$ rspec spec/part1_spec.rb:23`

0. Define a method `sum_to_n?(array, n)` that takes an array of integers and an additional integer, n, as arguments and returns true if any two elements in the array of integers sum to n. `sum_to_n?([], n)` should return false for any value of n, by definition. Run associated tests via: `$ rspec spec/part1_spec.rb:42`

You can check your progress on the all the above by running `$ rspec spec/part1_spec.rb`.

# 2. Strings and Regular Expressions

Check the documentation on String and Regexp as they could help tremendously with these exercises. :-)

0. Define a method `hello(name)` that takes a string representing a name and returns the string "Hello, " concatenated with the name. Run associated tests via: `$ rspec -e '#hello' spec/part2_spec.rb`

0. Define a method `starts_with_consonant?(s)` that takes a string and returns true if it starts with a consonant and false otherwise. (For our purposes, a consonant is any letter other than A, E, I, O, U.) NOTE: be sure it works for both upper and lower case and for nonletters! Run associated tests via: `$ rspec -e '#starts_with_consonant?' spec/part2_spec.rb`

0. Define a method `binary_multiple_of_4?(s)` that takes a string and returns true if the string represents a binary number that is a multiple of 4. NOTE: be sure it returns false if the string is not a valid binary number! Run associated tests via: `$ rspec -e '#binary_multiple_of_4?' spec/part2_spec.rb`

You can check your progress on the all the above by running `$ rspec spec/part2_spec.rb`.

# 3. Object Oriented Basics

Define a class `BookInStock` which represents a book with an ISBN number, `isbn`, and price of the book as a floating-point number, `price`, as attributes. Run associated tests via: `$ rspec -e 'getters and setters' spec/part3_spec.rb`

The constructor should accept the ISBN number (a string, since in real life ISBN numbers can begin with zero and can include hyphens) as the first argument and price as second argument, and should raise `ArgumentError` (one of Ruby's built-in exception types) if the ISBN number is the empty string or if the price is less than or equal to zero. Include the proper getters and setters for these attributes. Run associated tests via: `$ rspec -e 'constructor' spec/part3_spec.rb`

Include a method `price_as_string` that returns the price of the book formatted with a leading dollar sign and two decimal places, that is, a price of 20 should format as "$20.00" and a price of 33.8 should format as "$33.80". Run associated tests via: `$ rspec -e '#price_as_string' spec/part3_spec.rb`

You can check your progress on the all the above by running `rspec spec/part3_spec.rb`.

## More Challenges

* Try getting setup with an automated test framework such as [guard](http://code.tutsplus.com/tutorials/testing-your-ruby-code-with-guard-rspec-pry--cms-19974) or [autotest](https://rubygems.org/gems/autotest). Guard or AutoTest can be set up so that they will run all the tests in `spec/`, but every time you edit and save your code file, the tests are automatically re-run, so you don't have to run them manually. As we'll see later, this is the "watch the test fail" part of the TDD or test-driven process of development: write the tests before you write the code, watch the test fail, fill in the code and save the code file, then watch the test pass!

* Try pairing using the [one-undermanship pair programming style](http://www.agileventures.org/remote-pair-programming/pair-programming-protocols)