Data-Driven tests in RSpec

some_class_under_test.rb

class SomeClassUnderTest
  def some_method_under_test(input)
    input.to_s
  end
end

some_class_under_test_spec.rb

RSpec.describe SomeClassUnderTest do
  describe '#some_method_under_test' do
    subject { described_class.new.some_method_under_test input_value }

    [
      [ 'a string', '123', '123.00' ],
      [ 'an integer', 123, '123.00' ],
      [ 'a float', 123.0, '123.00' ],
      [ 'a negative number', -123, '-123.00' ],
      [ 'nil', nil, 'nil' ],
    ].each do |variation, input, expected_output|
      describe 'when the input is #{variation}' do
        let(:input_value) { input }
        it { is_expected.to eq(expected_output) }
      end
    end

    describe 'when the input is invalid' do
      let(:input_value) { 'invalid' }
      it { expect { subject }.to raise_error }
    end
  end
end