Introduction

RSpec stubs that work in isolation but fail within a Rails test suite are a common source of frustration. The issue typically stems from Rails' class reloading, method definition timing, or the difference between allow and expect when stubbing ActiveRecord queries.

Symptoms

  • allow(User).to receive(:find) does not intercept User.find(1)
  • Stub works in a unit test but not in an integration/request test
  • NoMethodError on a stubbed method in test
  • Stubbed return value is ignored, real database query executes
  • Intermittent test failures depending on test execution order

Example failing test: ```ruby # Test allow(User).to receive(:find).with(1).and_return(build_stubbed(:user)) expect(User.find(1)).to eq(user) # Fails: queries database instead

# Error ActiveRecord::RecordNotFound: Couldn't find User with 'id'=1 ```

Common Causes

  • Stub defined after the method is first called (class loaded before stub)
  • Using stub_model with class reloading in development mode
  • Stubbing a class method that is actually delegated through a proxy
  • Transactional fixtures rolling back the stub setup
  • Stubbing allow on a module that is included after the stub is set

Step-by-Step Fix

  1. 1.**Use allow_any_instance_of carefully, prefer class method stubs**:
  2. 2.```ruby
  3. 3.# Correct: stub the class method directly
  4. 4.allow(User).to receive(:find).with(1).and_return(user_double)

# Avoid this unless necessary: allow_any_instance_of(User).to receive(:some_method) ```

  1. 1.Ensure stub is set before the code under test runs:
  2. 2.```ruby
  3. 3.RSpec.describe UsersController do
  4. 4.before do
  5. 5.# Stub BEFORE any code loads the User class
  6. 6.allow(User).to receive(:find).and_raise("Unexpected User.find call")
  7. 7.allow(User).to receive(:find).with(1).and_return(build_stubbed(:user, id: 1))
  8. 8.end

it 'returns the user' do get :show, params: { id: 1 } expect(response).to have_http_status(:ok) end end ```

  1. 1.Stub method chains correctly:
  2. 2.```ruby
  3. 3.# For User.where(active: true).order(created_at: :desc).first
  4. 4.allow(User).to receive(:where).with(active: true).and_return(
  5. 5.double('relation', order: double('ordered', first: user))
  6. 6.)

# Or use receive_message_chain (less precise but simpler): allow(User).to receive_message_chain(:where, :order, :first).and_return(user) ```

  1. 1.Disable class reloading in test environment:
  2. 2.```ruby
  3. 3.# config/environments/test.rb
  4. 4.config.enable_reloading = false
  5. 5.config.cache_classes = true
  6. 6.`
  7. 7.**Use instance_double for stricter verification**:
  8. 8.```ruby
  9. 9.user = instance_double(User, id: 1, name: 'Test User')
  10. 10.allow(User).to receive(:find).with(1).and_return(user)
  11. 11.# This verifies that User actually has the stubbed methods
  12. 12.`

Prevention

  • Prefer instance_double over plain double for ActiveRecord objects
  • Use factories with build_stubbed instead of stubbing queries when possible
  • Keep stubs as close to the call site as possible in test setup
  • Add a test double verification: verify_doubled_constant_names = true
  • Document known stubbing issues in the team testing guide