Tools, Testing, and Style

Gems and Bundler

gem install bundler
bundle init
bundle add minitest
bundle install
bundle exec ruby app.rb

Gemfile declares dependencies. Gemfile.lock records exact versions. Use bundle exec so commands run with the versions from the lockfile.

Project Layout

my_app/
  Gemfile
  lib/
    my_app.rb
    my_app/user.rb
  test/
    user_test.rb

Small scripts can be one file. Reusable libraries usually put code under lib/ and tests under test/ or spec/.

Minitest

require "minitest/autorun"
require_relative "../lib/calculator"

class CalculatorTest < Minitest::Test
  def test_adds_numbers
    assert_equal 5, Calculator.add(2, 3)
  end
end

Minitest ships with Ruby. It is a good default for fundamentals and small libraries.

RSpec Shape

RSpec.describe Calculator do
  it "adds numbers" do
    expect(Calculator.add(2, 3)).to eq(5)
  end
end

RSpec is common in Rails apps and larger Ruby teams. It is expressive, but adds a dependency and its own DSL.

Style Conventions

snake_case_method
CamelCaseClass
SCREAMING_SNAKE_CASE = true

valid?     # predicate method
save!      # stricter or mutating version by convention
name=      # writer method

Use two spaces for indentation. Prefer clear method names, small objects, and direct Enumerable chains.

Mutation vs Non-Mutation

name = " ruby "
name.strip       # returns new string
name             # still " ruby "
name.strip!      # mutates name, returns nil if no change

arr.sort         # new sorted array
arr.sort!        # sort in place

Bang methods often mutate or raise more aggressively. Always check the documentation for the exact contract.

Debugging

p value                 # inspect to stdout
puts value.inspect
warn "message"          # stderr
caller.first            # current call location
raise "stop here"       # quick breakpoint-like stop

For real projects, use the debug gem available in modern Ruby versions.

Performance Basics

• Use String#<< or an array plus join for repeated string building.
• Use Set for many membership checks.
• Avoid repeated array.include? inside large loops when a hash or set would do.
• Prefer streaming files line by line with File.foreach for large files.
• Measure with Benchmark before rewriting clear code.

require "benchmark"
puts Benchmark.measure { 100_000.times { "ruby".upcase } }