[XP Training] Pair programming calculator problem

calculator.rb

class Calculator

  def calculate(input)
    splited =  split_string(input)
    mapped = splited.map(&:to_i)

    if (input.include?('+'))
      return mapped.reduce(:+)
    elsif (input.include?('-'))
      return mapped.reduce(:-)
    end
    input.to_i
  end

  def split_string(input)
    input_arr = input.split(/[+-]/)
  end

end

calculator_spec.rb

require_relative("Calculator")

context 'calculator' do

  before :all do
    @calculator = Calculator.new
  end

  it 'should return the input number' do
    expect(@calculator.calculate('5')).to eq 5
  end

  it 'should return the input number' do
    expect(@calculator.calculate('0')).to eq 0
  end

  it 'should add two numbers separated by the plus char' do
    expect(@calculator.calculate('5+5')).to eq 10
  end

  it 'should sum two or more numbers' do
    expect(@calculator.calculate('5+5+5+1')).to eq 16
  end

    it 'should sum two or more numbers separated by the plus char' do
    expect(@calculator.calculate('99+4+1+109')).to eq 213
  end

  it 'should subtract two numbers separated by the minus char' do
    expect(@calculator.calculate('5-1')).to eq 4
  end

end