Fast specs with Rails

faster_helper.rb

ENV["RAILS_ENV"] ||= 'test'

cur_dir = File.expand_path(File.dirname(__FILE__) + '/..')
$LOAD_PATH << "#{cur_dir}"

if defined? Rails
  # Most likely going with the full env
  puts "Running faster_helper with full Rails env..."
  # Eagerly load the Rails so that stubbed dependencies still work
  # http://stackoverflow.com/questions/11133712/using-rails-model-that-is-already-declared
  Rails.application.eager_load!
  require 'spec_helper'
else
  $LOAD_PATH << "#{cur_dir}/app/models"
  $LOAD_PATH << "#{cur_dir}/lib"

  require 'spec/support/rspec'
end

tax_spec.rb

# example of a spec

require 'faster_helper'
require 'investment_report/tax'

module InvestmentReport
  describe Tax, "#on_amount" do
    def self.tax_on(amount, &block)
      context "tax on #{amount}" do
        subject { Tax.on_amount(amount) }
        it(&block)
      end
    end

    def self.rate_on(amount, &block)
      context "tax rate on #{amount}" do
        subject { Tax.rate_on(amount) }
        it(&block)
      end
    end

    before { Tax.stub(medicare_levy_on: medicare_levy) }
    let(:medicare_levy) { 100 }

    context "<=6k: nil" do
      rate_on(0)    { should == 0 }
      tax_on(0)     { should == 0 }

      rate_on(3000) { should == 0 }
      tax_on(3000)  { should == 0 }

      rate_on(6000) { should == 0 }
      tax_on(6000)  { should == 0 }
    end

    context "6-37k: 15% over 6k plus medicare levy" do
      let(:medicare_levy) { 123456 }

      rate_on(6001)     { should == 0.15 }
      tax_on(6000.01)   { should be_within(0.01).of  0.01*0.15 + medicare_levy }

      tax_on(10_000)    { should be_within(0.01).of  4000*0.15 + medicare_levy }
      tax_on(37_000)    { should be_within(0.01).of  31_000*0.15 + medicare_levy }

      rate_on(37_000)   { should == 0.15 }
    end

    context "37-80k: $4650 plus 30% over $37000 plus medicare levy" do
      rate_on(37_001)   { should == 0.30 }

      tax_on(37_000.01) { should be_within(0.01).of  4650 + 0.01*0.3 + medicare_levy }
      tax_on(80_000)    { should be_within(0.01).of  4650 + 43_000*0.30 + medicare_levy }

      rate_on(80_000)   { should == 0.30 }
    end

    context "80-180k: $17,550 plus 37% over $80,000 plus medicare levy" do
      rate_on(80_001)   { should == 0.37 }

      tax_on(80_000.01) { should be_within(0.01).of  17_550 + 0.01*0.37 + medicare_levy }
      tax_on(100_000)   { should be_within(0.01).of  17_550 + 20_000*0.37  + medicare_levy }
      tax_on(180_000)   { should be_within(0.01).of  17_550 + 100_000*0.37  + medicare_levy }

      rate_on(180_000)   { should == 0.37 }
    end

    context "180+: $54,550 plus 45% over $180,000 plus medicare levy" do
      rate_on(180_001)    { should == 0.45 }

      tax_on(180_000.01)  { should be_within(0.01).of  54_550 + 0.01*0.45  + medicare_levy }
      tax_on(500_000)     { should be_within(0.01).of  54_550 + 320_000*0.45  + medicare_levy }

      rate_on(500_000)     { should == 0.45 }
    end
  end
end