rspec - 未找到命令

如何使用RSpec进行Ruby测试

bash
$ rspec --version

bash
$ gem install rspec

ruby
RSpec.describe Calculator do
  context "加法" do
    it "应该能够正确地加两个数字" do
      calculator = Calculator.new
      result = calculator.add(5, 7)
      expect(result).to eq(12)
    end
  end
  context "减法" do
    it "应该能够正确地减去两个数字" do
      calculator = Calculator.new
      result = calculator.subtract(10, 3)
      expect(result).to eq(7)
    end
  end
end

bash
$ rspec