Fed up with Rails fixtures? (part one)

Posted by James Mead Thu, 10 Aug 2006 04:09:00 GMT

In a previous post I explained why I’m not a big fan of Rails fixtures. But how can you avoid using them and still obtain good test coverage? Try forgetting about fixtures and writing unit tests that only test a single class and nothing else. Here’s an example where you hardly1 need to involve the database at all…

class Initial < ActiveRecord::Migration 
  def self.up 
    create_table :companies do |t| 
      t.column :name, :string 
    end
    create_table :employees do |t|
      t.column :company_id, :integer
      t.column :salary, :integer
    end
  end
end

class Company < ActiveRecord::Base
  has_many :employees
  def wage_bill
    employees.inject(0) { |total, employee| total + employee.salary }
  end
end

class Employee < ActiveRecord::Base
  belongs_to :company
end

So instead of writing this…

# companies.yml
walmart:
  id: 1
  name: Walmart

# employees.yml
fred:
  id: 1
  company_id: 1
  salary: 10000
anne:
  id: 2
  company_id: 1
  salary: 20000
class CompanyTest < Test::Unit::TestCase
  fixtures :companies, :employees
  def test_should_calculate_wage_bill
    assert_equal 30000, companies(:walmart).wage_bill
  end
end

You can write this…

class CompanyTest < Test::Unit::TestCase
  def test_should_calculate_wage_bill
    employees = []
    employees << Employee.new(:salary => 10000)
    employees << Employee.new(:salary => 20000)
    company = Company.new(:employees => employees)
    assert_equal 10000 + 20000, company.wage_bill
  end
end

This way you home in on the behaviour of the Company#wage_bill method and avoid testing the ActiveRecord code and access to the database. More ways to avoid hitting the database will follow in another post.

1 ActiveRecord still needs to know what columns in each table e.g.

SHOW FIELDS FROM companies

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Comments

  1. Marcus Ahnve said about 10 hours later:

    I’ve always had this nagging feeling that I did not like the fixtures, even though they seem so nice when you look at them. Good advice.

  2. Damien Tanner said 5 days later:

    That could sure speed up some tests. The issue is when your project has tens of models with lots of relationships.

  3. James Mead said 5 days later:

    Marcus: Thanks for the positive feedback.

    Damien: Are you saying there is an issue with with using fixtures or with the above technique when you have “tens of models with lots of relationships”? Our projects at Reevoo certainly come into that category and we use this technique (and many others including this) as much as we can to good effect.

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