Question

我正在学习rails（我主要是一名java开发人员），我的问题很明显，而且我在使用我的rspec测试访问模型上的方法时遇到了麻烦。我基本上遵循this tutorial，但将其应用于我自己的项目。我正在尝试将gradu_year定义为基于学生成绩和一年中当前时间的方法。当我实例化对象并在rails控制台中调用方法时，它可以像我期望的那样工作，但是当我在测试中尝试这样做时，我得到了：

undefined method `graduation_year'

student.rb

class Student < ActiveRecord::Base
  validates :school_id, presence: true, uniqueness: true
  validates :first_name, presence: true, length: { maximum: 30 }
  validates :last_name, presence: true, length: { maximum: 40 }
  validates :gender, presence: true, inclusion: { :in => %w(m f M F) }
  validates :grade, presence: true, numericality: { greater_than_or_equal_to: 1 , less_than_or_equal_to: 12 }

  def graduation_year
    year = Date.today.year + ( 12 - grade )
  end
end

student_spec.rb

require 'spec_helper'

describe Student do
  before { @student = Student.new(
                        school_id: 3, 
                        first_name: "Michael", 
                        last_name: "Green", 
                        gender: "M", 
                        grade: 6)}

  subject { @student }

  it { should respond_to(:school_id) }
  it { should respond_to(:first_name) }
  it { should respond_to(:last_name) }
  it { should respond_to(:gender) }
  it { should respond_to(:grade) }
  it { should respond_to(:graduation_year) }

  it { should be_valid }

  describe "when school_id is not present" do
    before { @student.school_id = " " }
    it { should_not be_valid }
  end
  .
  .
  .  
  describe "when grade is 7 graduation_year should be calculated correctly" do
    before { @student.grade = 7 }
    expect(@student.graduation_year).to eq(Date.today.year+5)
  end
end

错误消息

~/dev/rails_apps/spec/models/student_spec.rb:96:in `block (2 levels) in <top (required)>': undefined method `graduation_year' for nil:NilClass (NoMethodError)
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/example_group.rb:242:in `module_eval'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/example_group.rb:242:in `subclass'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/example_group.rb:228:in `describe'
from ~/dev/rails_apps/spec/models/student_spec.rb:94:in `block in <top (required)>'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/example_group.rb:242:in `module_eval'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/example_group.rb:242:in `subclass'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/example_group.rb:228:in `describe'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/dsl.rb:18:in `describe'
from ~/dev/rails_apps/spec/models/student_spec.rb:3:in `<top (required)>'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/configuration.rb:819:in `load'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/configuration.rb:819:in `block in load_spec_files'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/configuration.rb:819:in `each'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/configuration.rb:819:in `load_spec_files'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/command_line.rb:22:in `run'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/runner.rb:80:in `run'
from ~/dev/.rvm/gems/ruby-2.0.0-p247/gems/rspec-core-2.13.1/lib/rspec/core/runner.rb:17:in `block in autorun'

另外，我不认为这是问题，但我最初将graduation_year作为Student表上的属性，但删除了它，并且此测试应该验证它是否正确计算。 / p>

我在测试中也尝试了puts first_name，但是在first_name上我得到了相同的未定义方法错误。我想我只是错过了ruby / rails工作方式。

Answer 1

您的期望声明未包含在'it'子句中。试着写

describe "when grade is 7" do
  before { @student.grade = 7 }
  it 'calculates the graduation year correctly' do
    expect(@student.graduation_year).to eq(Date.today.year+5)
  end
end

作为旁注，以这种方式使用@student并不是惯用的。你最好使用一个定义学生的let语句。因此，与Student.new相比，您可以编写类似这样的内容：

let(:student) { Student.new(
                    school_id: 3, 
                    first_name: "Michael", 
                    last_name: "Green", 
                    gender: "M", 
                    grade: 6)}

所有随后对'@student'的引用都将替换为'student'。这可以确保描述块中没有任何泄漏。

let语句将记忆该对象，并且只有在规范中引用student时才会实例化该对象。

Answer 2

您无法直接在describe区块内设置期望值，就像您的行一样：

expect(@student.graduation_year).to eq(Date.today.year+5)

你没有说明你得到了什么具体的错误（即什么对象有未定义的方法），但此时@student将是nil，因为所有未定义的实例变量都是{{ 1}}，因此它不会有nil方法。但是，如果graduation_year是一个有效的表达式，那么@student.graduation_year调用就会得到一个未定义的方法。

Rails 4访问模型属性

student.rb

student_spec.rb

错误消息

2 个答案: