Rubyonrails Rspec期望()与期望{}

您好，我是RSpec的新手，我想弄清楚将块传递给Expect{}和只使用Expect()有什么不同.

下面是一个简单的例子

require "rails_helper"
RSpec.describe "Test",type: :model do
 it "testing count" do
   arr=[1,2,3]
   expect{arr<<1}.to change{arr.count}.by(1)
 end
end

这运行得很好，但当我执行此操作时

    require "rails_helper"
    RSpec.describe "Test",type: :model do
      it "testing count" do
        arr=[1,2,3]
        expect(arr<<1).to change{arr.count}.by(1)
      end
    end

它抛出一个错误

故障:

  1) Test testing count
     Failure/Error: expect(arr<<1).to change{arr.count}.by(1)
       expected `arr.count` to have changed by 1, but was not given a block
     # ./spec/models/test_spec.rb:6:in block (2 levels) in <top (required)>

即使我不使用带有零钱的块，它也会给我一个错误

require "rails_helper"
RSpec.describe "Test",type: :model do
  it "testing count" do
    arr=[1,2,3]
    expect{arr<<1}.to change(arr.count).by(1)
  end
end

故障:

  1) Test testing count
     Failure/Error: expect{arr<<1}.to change(arr.count).by(1)
     
     ArgumentError:
       `change` requires either an object and message (`change(obj, :msg)`) or a block (`change { }`). You passed an object but no message.

有没有人能解释一下为什么会这样？