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Testing Nested Attributes Assignment Implementation in factory_bot

This test suite examines FactoryBot’s handling of nested attributes in ActiveRecord associations, specifically focusing on the Post-Comment relationship. It validates the proper creation and assignment of nested comment attributes when creating Post objects, demonstrating FactoryBot’s integration with Rails’ accepts_nested_attributes_for functionality.

Test Coverage Overview

The test suite covers the essential aspects of nested attribute assignment in FactoryBot:

Default nested attributes creation with multiple comments
Override capability for nested attributes during factory creation
Validation of comment count in both default and override scenarios
Integration with ActiveRecord association mechanisms

Implementation Analysis

The testing approach utilizes RSpec’s describe/it blocks to structure the test cases. It employs FactoryBot’s define_model helper for dynamic model creation, establishing a Post-Comment relationship with nested attributes support. The implementation showcases sequence usage for unique comment bodies and attributes_for helper for building nested attributes.

Technical Details

Key technical components include:

RSpec testing framework
FactoryBot’s define_model and attributes_for helpers
ActiveRecord associations (has_many, belongs_to)
accepts_nested_attributes_for configuration
Dynamic model definition with string and text column types

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Clear test organization with before block setup
Isolated test cases for default and override scenarios
Proper use of factory sequences for unique data
Efficient model relationship testing
Clean and maintainable factory definitions

thoughtbot/factory_bot

spec/acceptance/nested_attributes_spec.rb

            
describe "association assignment from nested attributes" do
  before do
    define_model("Post", title: :string) do
      has_many :comments
      accepts_nested_attributes_for :comments
    end

    define_model("Comment", post_id: :integer, body: :text) do
      belongs_to :post
    end

    FactoryBot.define do
      factory :post do
        comments_attributes { [FactoryBot.attributes_for(:comment), FactoryBot.attributes_for(:comment)] }
      end

      factory :comment do
        sequence(:body) { |n| "Body #{n}" }
      end
    end
  end

  it "assigns the correct amount of comments" do
    expect(FactoryBot.create(:post).comments.count).to eq 2
  end

  it "assigns the correct amount of comments when overridden" do
    post = FactoryBot.create(:post, comments_attributes: [FactoryBot.attributes_for(:comment)])

    expect(post.comments.count).to eq 1
  end
end