with_model

with_model dynamically builds an Active Record model (with table) before each test in a group and destroys it afterwards.

Development status

with_model is actively maintained. It is quite stable, so while updates may appear infrequent, it is only because none are needed.

Installation

Install as usual: gem install with_model or add gem 'with_model' to your Gemfile. See .github/workflows/ci.yml for supported (tested) Ruby versions.

RSpec

Extend WithModel into RSpec:

require 'with_model'

RSpec.configure do |config|
  config.extend WithModel
end

minitest/spec

Extend WithModel into minitest/spec and set the test runner explicitly:

require 'with_model'

WithModel.runner = :minitest

class Minitest::Spec
  extend WithModel
end

Usage

After setting up as above, call with_model and inside its block pass it a table block and a model block.

require 'spec_helper'

describe "A blog post" do
  module MyModule; end

  with_model :BlogPost do
    # The table block (and an options hash) is passed to Active Record migration’s `create_table`.
    table do |t|
      t.string :title
      t.timestamps null: false
    end

    # The model block is the Active Record model’s class body.
    model do
      include MyModule
      has_many :comments
      validates_presence_of :title

      def self.some_class_method
        'chunky'
      end

      def some_instance_method
        'bacon'
      end
    end
  end

  # with_model classes can have associations.
  with_model :Comment do
    table do |t|
      t.string :text
      t.belongs_to :blog_post
      t.timestamps null: false
    end

    model do
      belongs_to :blog_post
    end
  end

  it "can be accessed as a constant" do
    expect(BlogPost).to be
  end

  it "has the module" do
    expect(BlogPost.include?(MyModule)).to eq true
  end

  it "has the class method" do
    expect(BlogPost.some_class_method).to eq 'chunky'
  end

  it "has the instance method" do
    expect(BlogPost.new.some_instance_method).to eq 'bacon'
  end

  it "can do all the things a regular model can" do
    record = BlogPost.new
    expect(record).not_to be_valid
    record.title = "foo"
    expect(record).to be_valid
    expect(record.save).to eq true
    expect(record.reload).to eq record
    record.comments.create!(:text => "Lorem ipsum")
    expect(record.comments.count).to eq 1
  end

  # with_model classes can have inheritance.
  class Car < ActiveRecord::Base
    self.abstract_class = true
  end

  with_model :Ford, superclass: Car do
  end

  it "has a specified superclass" do
    expect(Ford < Car).to eq true
  end
end

describe "with_model can be run within RSpec :all hook" do
  with_model :BlogPost, scope: :all do
    table do |t|
      t.string :title
    end
  end

  before :all do
    BlogPost.create # without scope: :all these will fail
  end

  it "has been initialized within before(:all)" do
    expect(BlogPost.count).to eq 1
  end
end

describe "another example group" do
  it "does not have the constant anymore" do
    expect(defined?(BlogPost)).to be_falsy
  end
end

describe "with table options" do
  with_model :WithOptions do
    table :id => false do |t|
      t.string 'foo'
      t.timestamps null: false
    end
  end

  it "respects the additional options" do
    expect(WithOptions.columns.map(&:name)).not_to include("id")
  end
end

Requirements

See the gemspec metadata for dependency requirements. RSpec and minitest are indirect dependencies, and with_model should support any maintained version of both.

Thread-safety

A unique table name is used for tables generated via with_model/WithModel::Model.new. This allows with_model (when limited to this API) to run concurrently (in processes or threads) with a single database schema. While there is a possibility of collision, it is very small.
A user-supplied table name is used for tables generated via with_table/WithModel::Table.new. This may cause collisions at runtime if tests are run concurrently against a single database schema, unless the caller takes care to ensure the table names passed as arguments are unique across threads/processes.
Generated models are created in stubbed constants, which are global; no guarantee is made to the uniqueness of a constant, and this may be unsafe.
Generated classes are Active Record subclasses:
- This library makes no guarantee as to the thread-safety of creating Active Record subclasses concurrently.
- This library makes no guarantee as to the thread-safety of cleaning up Active Record/Active Support’s internals which are polluted upon class creation.

In general, with_model is not guaranteed to be thread-safe, but is, in certain usages, safe to use concurrently across multiple processes with a single database schema.

Versioning

with_model uses Semantic Versioning 2.0.0.