Refactoring ruby brownbag

fizzbuzz.rb

class FizzBuzz
  def self.evaluate(number)
    raise "Not a number" unless number.is_a? Integer
    return "fizzbuzz" if number % 5 == 0 && number % 3 == 0
    return "fizz" if number % 3 == 0
    return "buzz" if number % 5 == 0
    number.to_s
  end
end

describe FizzBuzz do

  describe "#evaluate" do

    it 'evaluates a number' do
      expect { described_class.evaluate(1) }.to_not raise_error "Not a number"
    end

    it 'raises an error when not given an Integer' do
      expect { described_class.evaluate("not a number") }.to raise_error "Not a number"
    end

    context "when given a number not divisible by 3 or 5" do
      it { expect(described_class.evaluate(7)).to eql "7" }
    end

    context "when given a number divisible by 3" do
      it { expect(described_class.evaluate(3)).to eql "fizz" }
      it { expect(described_class.evaluate(9)).to eql "fizz" }
    end

    context "when given a number divisible by 5" do
      it { expect(described_class.evaluate(5)).to eql "buzz" }
      it { expect(described_class.evaluate(10)).to eql "buzz" }
    end

    context "when given a number divisible by 3 and 5" do
      it { expect(described_class.evaluate(15)).to eql "fizzbuzz" }
      it { expect(described_class.evaluate(30)).to eql "fizzbuzz" }
    end

  end
end