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Testing Lazy Configuration Model Implementation in rails_admin

This test suite validates the lazy loading functionality in RailsAdmin’s configuration system, specifically focusing on the LazyModel class. It ensures proper initialization, block evaluation timing, and method delegation behavior.

Test Coverage Overview

The test suite provides comprehensive coverage of the LazyModel initialization and configuration mechanics.

Tests lazy evaluation of configuration blocks
Verifies block execution timing and caching
Covers deferred block handling
Tests method delegation with Kernel conflicts

Implementation Analysis

The testing approach employs RSpec’s expectation and spy mechanisms to verify lazy loading behavior. It uses mock objects and execution tracking to ensure configuration blocks are evaluated at the correct time and only once.

Uses RSpec’s expect_any_instance_of for method call verification
Implements before/after hooks for Kernel method testing
Utilizes let blocks for test setup isolation

Technical Details

RSpec as the testing framework
Mock objects for configuration verification
Module evaluation for Kernel method testing
Spy mechanisms for tracking method calls
Block-based configuration testing

Best Practices Demonstrated

The test suite exemplifies several testing best practices in Ruby and RSpec.

Isolated test contexts
Proper cleanup of modified global state
Clear test case organization
Effective use of RSpec’s subject and let blocks
Comprehensive edge case coverage

railsadminteam/rails_admin

spec/rails_admin/config/lazy_model_spec.rb

            
# frozen_string_literal: true

require 'spec_helper'

RSpec.describe RailsAdmin::Config::LazyModel do
  subject { RailsAdmin::Config::LazyModel.new(:Team, &block) }
  let(:block) { proc { register_instance_option('parameter') } } # an arbitrary instance method we can spy on

  describe '#initialize' do
    it "doesn't evaluate the block immediately" do
      expect_any_instance_of(RailsAdmin::Config::Model).not_to receive(:register_instance_option)
      subject
    end

    it 'evaluates block when reading' do
      expect_any_instance_of(RailsAdmin::Config::Model).to receive(:register_instance_option).with('parameter')
      subject.groups # an arbitrary instance method on RailsAdmin::Config::Model to wake up lazy_model
    end

    it 'evaluates config block only once' do
      expect_any_instance_of(RailsAdmin::Config::Model).to receive(:register_instance_option).once.with('parameter')

      subject.groups
      subject.groups
    end
  end

  describe '#add_deferred_block' do
    let(:another_block) { proc { register_instance_option('parameter2') } }

    it "doesn't evaluate the block immediately" do
      expect_any_instance_of(RailsAdmin::Config::Model).not_to receive(:register_instance_option).with('parameter2')
      subject.add_deferred_block(&another_block)
    end

    it 'evaluates the block immediately after initialization' do
      subject.target
      expect_any_instance_of(RailsAdmin::Config::Model).to receive(:register_instance_option).with('parameter2')
      subject.add_deferred_block(&another_block)
    end
  end

  context 'when a method is defined in Kernel' do
    before do
      Kernel.module_eval do
        def weight
          42
        end
      end
    end

    after do
      Kernel.module_eval do
        undef weight
      end
    end

    it 'proxies calls for the method to @object' do
      expect(subject.weight).to eq 0
    end
  end
end