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Ruby Intro

This 3-part homework gives some basic practice in Ruby as well as getting you accustomed to making testing a regular part of your workflow.

NOTE: do not fork this repo. Click the "Use this template" button then clone the repo that it generates

Learning Goals

After completing this assignment, you will be able to:

  • Write simple code that uses basic constructs in the Ruby language, including methods and arguments, conditionals, string and array manipulation, regular expressions, and basic object-oriented programming mechanisms
  • Describe the Ruby project conventions for where code files and test files are located in a project's directory hierarchy
  • Run individual tests or suites of tests using the RSpec unit testing tool
  • Describe the basic syntax of RSpec unit tests

Overview

You may find the Ruby documentation at 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 will 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.

Ruby Install and Setup Instructions

Install Ruby. (I recommend rbenv, in particular the rbenv-installer tool.)

The current stable version of ruby is: 3.3.4
The ruby version on Gradescope is: 3.0.2p107

Running RSpec

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

Run rspec now. You should see 34 examples, 20 failures in red.

Runing rspec with no arguments will execute the tests in all the files spec/*_spec.rb. 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, run rspec spec/part1_spec.rb.

Run rspec spec/part1_spec.rb. You should see 12 examples, 9 failures in red.

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

1. Arrays, Hashes, and Enumerables

Check the Ruby 3.x documentation on Array, Hash and Enumerable as they could help tremendously with these exercises. Various Ruby cheatsheets are also helpful as a quick reference! Although Ruby supports looping constructs like 'for' and 'while', consider using block syntax with each for a more idiomatic use of Ruby.

sum

The method sum(arr) should return the sum of the values in arr.

  1. Run the tests: rspec -fd -e '#sum ' spec/part1_spec.rb. You should see 3 examples, 2 failures in red.
    • Problem? Make sure you are in the correct directory: cd assignment and RSpec is installed.
  2. Read the RSpec report.
  3. Pick one of the failures to correct. (In fact, we could "fix" both at the same time)
    • Suppose we pick expect(sum([1, 2, 3, 4, 5])).to be_a_kind_of Integer.
  4. Add just enough code to the method sum(array) in lib/ruby_intro.rb to pass the selected test.
    • The simplest code we can add is to return a constant. Let's return 0. Because Ruby is neat, we can do this by simply putting 0 in the function body:
    def sum(arr)
  0
end
  5. Re-run the tests: rspec -fd -e '#sum ' spec/part1_spec.rb. You should see 3 examples, 1 failure in red.
  6. Add and commit changes: git add . && git commit -m "improved correctness of sum"
  7. Read the RSpec report.
  8. Pick one of the failures to correct. (Pick the only failure...)
  9. Add just enough code to pass the test.
  10. Re-run the tests. You should see 3 examples, 0 failures in green.
    • Yay?
      • Yay!
      • Add and commit changes: git add . && git commit -m "sum is passing all tests"
      • Push changes: git push
    • Nay?
      • Go back to step 6 and Try Harder.

max_2_sum

The method max_2_sum(arr) should return the sum of its two largest elements in arr.

  1. Run the tests: rspec -fd -e '#max_2_sum' spec/part1_spec.rb. You should see 5 examples, 4 failures in red.
  2. Read the RSpec report.
  3. Pick one of the failures to correct.
  4. Add just enough code to pass the selected test.
  5. Add and commit changes: git add . && git commit -m "<comment>"
  6. Until all tests are passing (0 failures), go back to step 0.
  7. Push changes: git push

sum_to_n?

The method sum_to_n?(arr, n) takes an array of integers arr and an additional integer, n, as arguments and returns true if any two elements in arr sum to n.

  1. Run the tests: rspec -fd -e '#sum_to_n?' spec/part1_spec.rb.
  2. Read the RSpec report.
  3. Pick one of the failures to correct.
  4. Add just enough code to pass the selected test.
  5. Add and commit changes.
  6. Until all tests are passing (0 failures), go back to step 0.
  7. Push changes.

Finally

Check your progress on all Part 1 methods: rspec -fd spec/part1_spec.rb. All tests should be green.

Now is a good time (and the right time) to go back and consider how you can improve your code? Might there be a better way (a more rubyistic / efficient / readable / etc.) to implement the methods? Try at least 1 alternative solution (with a focus on making the solution use more of Ruby's language features) for each method. Settle on the one you like the best.

2. Strings and Regular Expressions

Check the documentation on String and Regexp as they could help tremendously with these exercises. For future reference as well, check out Rubular for regex related queries.

  1. 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.

    • Everytime a new test passes, add and commit changes: git add . && git commit -m "<comment>"
    • Once all tests are passing, push changes: git push

  2. 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 English letter other than A, E, I, O, U.) Make sure it works for both upper and lower case and for non-letters. Run associated tests via: rspec -e '#starts_with_consonant?' spec/part2_spec.rb.

    • Everytime a new test passes, add and commit changes: git add . && git commit -m "<comment>"
    • Once all tests are passing, push changes: git push

  3. 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, such as '1000'. Make 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.

    • Everytime a new test passes, add and commit changes: git add . && git commit -m "<comment>"
    • Once all tests are passing, push changes: git push

You can check your progress on all of the above by running rspec -fd spec/part2_spec.rb. All tests should be green.

Consider ways to improve your code.

3. Object Oriented Basics

Remember:

  • Everytime a new test passes, add and commit changes: git add . && git commit -m "<comment>"
  • Once all tests are passing, push changes: git push

  1. Implement the constructor for class BookInStock which represents a book with an ISBN number, isbn, and price of the book, price. 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 (a floating point number) as the second argument. Also implement the getter and setter methods for isbn and price. Run associated tests via: rspec -e 'getters and setters' spec/part3_spec.rb

  2. The constructor 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. Run associated tests via: rspec -e 'constructor' spec/part3_spec.rb

  3. Implement the method BookInStock#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. Check out formatted string methods in Ruby. Run associated tests via: rspec -e '#price_as_string' spec/part3_spec.rb

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

Finally

Generate a test log file using rspec -fd -o <LastName>_<FirstName>_PA1.txt spec/, where <LastName> and <FirstName> are your last and first names, respectively. This will put the entire RSpec report into one file.

Don't forget to add, commit, and push!

More Challenges

  • I strongly recommend that you conform to a Ruby style guide: gem install rubocop, then run rubocop [list of filenames to check].

  • Try getting setup with an automated test framework such as guard or 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 you should have seen in this assignment, 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!