如果您已经阅读了RSpec Doubles部分，那么您已经看到了RSpec Stubs，它是一种特殊类型的方法，代表现有方法或尚不存在的方法。

这是RSpec Doubles部分中的代码-

class ClassRoom 
   def initialize(students) 
      @students=students 
   End
   
   def list_student_names 
      @students.map(&:name).join(',') 
   end 
end 

describe ClassRoom do 
   it 'the list_student_names method should work correctly' do 
      student1=double('student') 
      student2=double('student') 
      
      allow(student1).to receive(:name) { 'John Smith'}
      allow(student2).to receive(:name) { 'Jill Smith'} 
      
      cr=ClassRoom.new [student1,student2]
      expect(cr.list_student_names).to eq('John Smith,Jill Smith') 
   end 
end

在无涯教程的示例中，allow()方法提供了测试ClassRoom类所需的方法。在这种情况下，需要一个对象，其行为类似于Student类，但是该类实际上并不存在。知道Student类需要提供一个name()方法，并且使用allow()为name()创建一个方法。

需要注意的一件事是，多年来RSpec的语法发生了一些变化。在较旧的RSpec版本中，上述方法存根的定义如下:

student1.stub(:name).and_return('John Smith') 
student2.stub(:name).and_return('Jill Smith')

采用上面的代码，并用旧的RSpec语法替换两条 allow()行-

class ClassRoom 
   def initialize(students) 
      @students=students 
   end 
   
   def list_student_names 
      @students.map(&:name).join(',') 
   end 
	
end 

describe ClassRoom do 
   it 'the list_student_names method should work correctly' do 
      student1=double('student') 
      student2=double('student')
      
      student1.stub(:name).and_return('John Smith')
      student2.stub(:name).and_return('Jill Smith') 
      
      cr=ClassRoom.new [student1,student2] 
      expect(cr.list_student_names).to eq('John Smith,Jill Smith') 
   end 
end

执行上面的代码时，您将看到此输出-

.
Deprecation Warnings:

Using `stub` from rspec-mocks' old `:should` syntax without explicitly 
   enabling the syntax is deprec 

ated. Use the new `:expect` syntax or explicitly enable `:should` instead. 
   Called from C:/rspec_tuto 

rial/spec/double_spec.rb:15:in `block (2 levels) in <top (required)>'.
If you need more of the backtrace for any of these deprecations 
   to identify where to make the necessary changes, you can configure 

`config.raise_errors_for_deprecations!`, and it will turn the 
   deprecation warnings into errors, giving you the full backtrace.

1 deprecation warning total

Finished in 0.002 seconds (files took 0.11401 seconds to load)
1 example, 0 failures

建议您在RSpec示例中创建方法Stubs时使用新的allow()语法。

参考链接

https://www.learnfk.com/rspec/rspec-stubs.html