问rspec错误-没有要加载的此类文件-- rspec/mocks (LoadError)

EN

/usr/lib/ruby/vendor_ruby/rspec/core/mocking/
with_rspec.rb:1:in `require': no such file to load -- rspec/mocks (LoadError)

describe "It should return the parameter that was passed in" do
  it "should return 20 when 20 is passed in" do
    a = fb(20)
    a.should == 20
  end
  it "should return 30 when 30 is passed in" do
    a = fb(30)
    a.should == 30
  end
end

def fb(n)
  n
end