ActiveMocker creates mock classes from ActiveRecord models, allowing your test suite to run at breakneck speed. This can be done by not loading Rails or hitting a database. The models are read dynamically and statically so that ActiveMocker can generate a Ruby file to require within a test. The mock file can be run by itself and comes with a partial implementation of ActiveRecord. Attributes and associations can be used the same as in ActiveRecord. Methods have the same argument signature but raise a NotImplementedError when called, allowing you to stub it with a mocking framework, like RSpec. Mocks are regenerated when the schema is modified so your mocks won't go stale, preventing the case where your units tests pass but production code fails.

Examples from a real apps

Code Quality Rank: L4
Monthly Downloads: 2,971
Programming language: Ruby
License: MIT License
Tags: Testing     Mock     Projects    
Latest version: v2.6.2

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Creates stub classes from any ActiveRecord model.

By using stubs in your tests you don't need to load Rails or the database, sometimes resulting in a 10x speed improvement.

ActiveMocker analyzes the methods and database columns to generate a Ruby class file.

The stub file can be run standalone and comes included with many useful parts of ActiveRecord.

Stubbed out methods contain their original argument signatures or ActiveMocker's friendly code can be brought over in its entirety.

Mocks are regenerated when the schema is modified so your mocks won't go stale, preventing the case where your unit tests pass but production code fails.

Examples from a real app

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Add this line to your application's Gemfile:

group :development, :test do
  gem 'active_mocker'

It needs to be in development as well as test groups, as the development environment is where mocks will be generated. Then execute:

$ bundle

Or install it yourself as:

$ gem install active_mocker


  • Tested with Rails 4.x, 5.x, 6.x
  • Requires Ruby MRI >= 2.4.x


See example_rails_app for complete setup.

Generate Mocks

Running this rake task builds/rebuilds the mocks. It will be ran automatically after every schema modification. If the model changes, this rake task needs to be called manually. You could add a file watcher for when your models change and have it run the rake task.

rake active_mocker:build



ActiveRecord::Schema.define(version: 20140327205359) do

  create_table "people", force: true do |t|
    t.integer  "account_id"
    t.string   "first_name",        limit: 128
    t.string   "last_name",         limit: 128
    t.string   "address",           limit: 200
    t.string   "city",              limit: 100



class Person < ActiveRecord::Base
  belongs_to :account

  def self.bar(name, type=nil)
    puts name


Using With Rspec, --tag active_mocker:true

require 'rspec'
require 'active_mocker/rspec_helper'
require 'spec/mocks/person_mock'
require 'spec/mocks/account_mock'

describe 'Example', active_mocker:true do

  before do
    Person.create # stubbed for PersonMock.create


  • Assigning the tag active_mocker:true will stub any ActiveRecord model Constants for Mock classes in an it or a before/after(:each). This removes any need for dependency injection. Write tests and code like you would normally.
  • To stub any Constants in before(:all), after(:all) use active_mocker.find('ClassName').
  • Mock state will be cleaned up for you in an after(:all). To clean state by yourself, use active_mocker.delete_all.

  => ["id", "account_id", "first_name", "last_name", "address", "city"]

person = Person.new( first_name:  "Dustin", 
                     last_name:   "Zeisler", 
                     account:      Account.new )
  => "#<PersonMock id: nil, account_id: nil, first_name: "Dustin", last_name: "Zeisler", address: nil, city: nil>"

  => "Dustin"

When schema.rb changes, the mock fails

(After rake db:migrate is called the mocks will be regenerated.)


ActiveRecord::Schema.define(version: 20140327205359) do

  create_table "people", force: true do |t|
    t.integer  "account_id"
    t.string   "f_name",        limit: 128
    t.string   "l_name",        limit: 128
    t.string   "address",       limit: 200
    t.string   "city",          limit: 100


Person.new(first_name: "Dustin", last_name: "Zeisler")
  =>#<UnknownAttributeError unknown attribute: first_name >

Creating Custom collections

If you want to create a custom set of records that is not part of the global collection for model. (ie. for stubbing in a test)

User::ScopeRelation.new([User.new, User.new])

This gives the full query API (ie. find_by, where, etc).

This is not a feature available in ActiveRecord, so do not include this where you intend to swap for ActiveRecord.

Optional Features

Use theses defaults if you are starting fresh



Enables created_at and updated_at to be updated on save and create


When using "active_mocker/rspec_helper", it deletes all records from all mocks before each example.


When requiring "active_mocker/rspec_helper", and adding active_mocker: true to the describe metadata, these errors will be auto stubbed:

  • ActiveRecord::RecordNotFound
  • ActiveRecord::RecordNotUnique
  • ActiveRecord::UnknownAttributeError

Copy over Mock safe methods into the generated mock

Adding the comment ActiveMocker.safe_methods at the top of a class marks it as safe to copy to the mock. Be careful. It should not contain anything that ActiveMocker cannot run.

  # ActiveMocker.safe_methods(scopes: [], instance_methods: [:full_name], class_methods: [])
  class User
    def full_name
      "#{first_name} + #{last_name}"

Mocking Methods

Rspec 3 Mocks - verify double

Verifying doubles is a stricter alternative to normal doubles that provides guarantees about what is being verified. When using verifying doubles, RSpec will check if the methods being stubbed are actually present on the underlying object if it is available. rspec-mocks/docs/verifying-doubles

RSpec.configure do |config|
  config.mock_framework = :rspec
  config.mock_with :rspec do |mocks|
    mocks.verify_doubled_constant_names = true
    mocks.verify_partial_doubles = true
  => NotImplementedError: ::bar is not Implemented for Class :PersonMock. To continue stub the method.

allow(Person).to receive(:bar) do |name, type=nil|
  "Now implemented with #{name} and #{type}"

Person.bar('foo', 'type')
=> "Now implemented with foo and type"
When the model changes, the mock fails

(Requires a regeneration of the mocks files.)


class Person < ActiveRecord::Base
  belongs_to :account

  def self.bar(name)
    puts name


Person.bar('foo', 'type')
  => ArgumentError: wrong number of arguments (2 for 1)


class Person < ActiveRecord::Base
  belongs_to :account

  def self.foo(name, type=nil)
    puts name


allow(Person).to receive(:bar) do |name, type=nil|
  "Now implemented with #{name} and #{type}"
=> RSpec::Mocks::MockExpectationError: PersonMock does not implement: bar

Constants and Modules

  • Any locally defined modules will not be included or extended. It can be disabled by ActiveMocker::Config.disable_modules_and_constants = true

class Person < ActiveRecord::Base

  => 13

Scoped Methods

  • Any chained scoped methods will be available when the mock file that defines it is required. When called, it raises a NotImplementedError. Stub the method with a value to continue.

Managing Mocks

require "active_mocker/rspec_helper"

active_mocker.delete_all # Delete all records from loaded mocks

active_mocker.find("User") # Find a mock by model name. Useful in before(:all)/after(:all) where automatic constant stubbing is unavailable.

active_mocker.mocks.except("User").delete_all # Delete all loaded mock expect the User mock.

ActiveRecord supported methods

See Documentation for a complete list of methods and usage.

Class Methods - docs

  • new
  • create/create!
  • column_names/attribute_names
  • delete_all/destroy_all
  • table_name
  • slice
  • alias_attributes

Query Methods - docs

  • all
  • find
  • find_by/find_by!
  • find_or_create_by
  • find_or_initialize_by
  • where(conditions_hash)
  • where(key: array_of_values)
  • where.not(conditions_hash)
  • delete_all/destroy_all
  • delete_all(conditions_hash)
  • destroy(id)/delete(id)
  • update_all
  • update(id, attributes)
  • count
  • uniq
  • first/last
  • average(:field_name)
  • minimum(:field_name)
  • maximum(:field_name)
  • sum(:field_name)
  • order(:field_name)
  • reverse_order
  • limit
  • none

Relation Methods - docs

  • concat
  • include
  • push
  • clear
  • take
  • empty?
  • replace
  • any?
  • many?

instance methods - docs

  • attributes
  • update
  • save/save!
  • write_attribute/read_attribute
  • delete
  • new_record?
  • persisted?
  • reload
  • attribute_names
  • attribute_present?
  • has_attribute?
  • slice
  • attribute_alias?
  • alias_attributes
  • touch


  • build_< association >
  • create_< association >
  • create_< association >!
  • < association >.create
  • < association >.build

Schema/Migration Option Support

  • A db/schema.rb is not required.
  • All schema types are supported and coerced by Virtus. If coercion fails, the passed value will be retained.
  • Default value is supported.
  • Scale and Precision are not supported.

Known Limitations

  • Namespaced modules are not currently supported.
  • When an association is set in one object it may not always be reflective in other objects, especially when it is a non standard/custom association. See test_rails_4_app/spec/active_record_compatible_api.rb for a complete list of supported associations.
  • Validation/Callbacks are not supported.
  • Sql queries, joins, etc will never be supported.
  • A record that has been created and then is modified will persist changes without calling #save. Beware of this difference.
  • This is not a full replacement for ActiveRecord.
  • Primary key will always default to id. If this is causing a problem, feel free to open an issue (or even better, a PR =)).


Thanks to Jeff Olfert for being my original inspiration for this project.


Your contributions are welcome!

  1. Fork it ( http://github.com/zeisler/active_mocker/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request