Automatic generation of rspec model tests and factories for factory girl

models.rb

class Models
  def self.generate what = :model
    Rails.application.eager_load!
    ActiveRecord::Base.descendants.each do |model|
      method(what)[model]
    end
    true
  end
  def self.factory model
    factory_file_name = "spec/factories/#{model.name.underscore}.rb"
    unless File.exists?(factory_file_name)
      File.open(factory_file_name,"w") do |file|
        factory_for model, file
      end
    end
  end
  def self.factory_for model, file
    file << <<-EOT
FactoryBot.define do
  factory :#{model.name.underscore}, :class => '#{model.name}' do
#{factory_cols model}
  end
end
    EOT
  end
  def self.factory_cols model
    associations = model.reflections
    "".tap do |output_text|
      model.columns.each do |col|
        next if col.name == 'id'
        stripped_name = col.name.gsub(/_id$/,'').to_sym
        output_text << "\n    "
        assoc =  associations[stripped_name]
        if assoc && [:has_one,:belongs_to].include?(assoc.macro)
          output_text << if assoc.options[:class_name]
            "association :#{stripped_name.to_s}, factory: :#{assoc.options[:class_name].underscore}"
          else
            stripped_name.to_s
          end
        else
          output_text << "#{preprocess_name col.name, col.type } #{factory_default_for(col.name, col.type)}"
        end
      end
    end
  end
  def self.preprocess_name name, type
    case name
    when /retry/
      "self.#{name}"
    when /e.*mail/,/name/
      if [:text,:string].include?(type)
        "sequence(:#{name})"
      else
        name
      end
    else
      name
    end
  end
  def self.factory_default_for name, type
    case type
    when :integer, :decimal
      "1"
    when :date
      "Time.now.to_date"
    when :datetime
      "Time.now"
    when :boolean
      "true"
    when :spatial
      "nil"
    else
      case name
       when /e.*mail/
         '{ |n| "test#{n}@example.com" }'
       when /name/
         '{ |n| "name#{n}" }'
       when /country/
         '"GB"'
       when /_ip$/
        '"192.168.0.1"'
       when /phone/
        '"+44000000000"'
      else
        '"test123"'
       end
    end
  end
  def self.model model
    test_file_name = "spec/models/#{model.name.underscore}_spec.rb"
    unless File.exists?(test_file_name)
      File.open(test_file_name,"w") do |file|
        describe_model model, file
      end
    end
  end
  def self.describe_model model, file
    file << <<-EOT
require 'rails_helper'

describe #{model.name}, :type => :model do
  # let (:subject) { build :#{model.name.underscore} }
#{read_write_tests model}
#{associations model.reflections}
end
  EOT
  end
  def self.read_write_tests model
    "  context \"validation\" do".tap do |output_text|
      model.validators.select { |val| val.is_a? ActiveModel::Validations::PresenceValidator }.map(&:attributes).
       flatten.each { |col| output_text << "\n    it { should validate_presence_of :#{col} }"}
      model.validators.select { |val| !val.is_a? ActiveModel::Validations::PresenceValidator }.
       each { |col| output_text << "\n    it \"#{col.class.to_s.demodulize.underscore} test for #{col.attributes.map(&:to_sym).to_s}\""}
    end << "\n  end"
  end
  def self.associations reflections
    "  context \"associations\" do".tap do |output_text|
      reflections.each_pair { |key,assoc| output_text << "\n    it { should #{translate_assoc assoc.macro} :#{test_assoc_name assoc} }"}
    end << "\n  end"
  end
  def self.translate_assoc macro
    macro.to_s.gsub(/belongs/,'belong').gsub(/has/,'have')
  end
  def self.test_assoc_name assoc
    case assoc.macro
    when /have_many/
      assoc.plural_name
    when /has_one/,/belongs_to/
      assoc.name
    else
      assoc.name
    end
  end
end

Assumes you have the shoulda matchers as well.

Fire up the rails console

load 'models.rb'
Models.generate :factory
Models.generate :models

Existing files are left alone.

It creates tests for all of the existing relationships and mandatory columns, plus the validations it doesn't understand are set up as pending tests.

It's a way forward if you have no tests at all.

Here is a version I worked on more recently that uses the file system instead of calling eager_load!. It came out of needing something that would work with engines and incomplete dependencies.

bundle exec rails runner "load '../models.rb' ; error = Models.generate([:model,:factory]) rescue \$! ; puts error.backtrace.join(\"\\n\") if error.respond_to?(:backtrace)"

class Models
  def self.generate what = :model
    require_models.each do |model|
      Array(what).each { |call_method| method(call_method)[model] }
    end
    true
  end

  def self.factory model
    factory_file_name = "spec/factories/#{model.name.underscore}.rb"
    unless File.exists?(factory_file_name)
      FileUtils.mkdir_p(File.dirname(factory_file_name))
      File.open(factory_file_name, "w") do |file|
        factory_for model, file
      end
    end
  end

  def self.factory_for model, file
    file << <<-EOT
FactoryBot.define do
  factory :#{model.name.underscore}, :class => '#{model.name}' do
#{factory_cols model}
  end
end
    EOT
  end

  def self.factory_cols model
    associations = model.reflections
    "".tap do |output_text|
      model.columns.each do |col|
        next if col.name == 'id'
        stripped_name = col.name.gsub(/_id$/, '').to_sym
        output_text << "\n    "
        assoc = associations[stripped_name]
        if assoc && [:has_one, :belongs_to].include?(assoc.macro)
          output_text << if assoc.options[:class_name]
                           "association :#{stripped_name.to_s}, factory: :#{assoc.options[:class_name].underscore}"
                         else
                           stripped_name.to_s
                         end
        else
          output_text << "#{preprocess_name col.name, col.type } #{factory_default_for(col.name, col.type)}"
        end
      end
    end
  end

  def self.preprocess_name name, type
    case name
    when /retry/
      "self.#{name}"
    when /e.*mail/, /name/
      if [:text, :string].include?(type)
        "sequence(:#{name})"
      else
        name
      end
    else
      name
    end
  end

  def self.factory_default_for name, type
    case type
    when :integer, :decimal
      "1"
    when :date
      "Time.now.to_date"
    when :datetime
      "Time.now"
    when :boolean
      "true"
    when :spatial
      "nil"
    else
      case name
      when /e.*mail/
        '{ |n| "test#{n}@example.com" }'
      when /name/
        '{ |n| "name#{n}" }'
      when /country/
        '"GB"'
      when /_ip$/
        '"192.168.0.1"'
      when /phone/
        '"+44000000000"'
      else
        '"test123"'
      end
    end
  end

  def self.model model
    test_file_name = "spec/models/#{model.name.underscore}_spec.rb"
    unless File.exists?(test_file_name)
      FileUtils.mkdir_p(File.dirname(test_file_name))
      File.open(test_file_name, "w") do |file|
        describe_model model, file
      end
    end
  end

  def self.describe_model model, file
    file << <<-EOT
require 'rails_helper'

describe #{model.name}, :type => :model do
  # let (:subject) { build :#{model.name.underscore} }
#{read_write_tests model}
#{associations model.reflections}
#{methods model}
end
    EOT
  end

  def self.read_write_tests model
    "  context \"validation\" do".tap do |output_text|
      model.validators.select { |val| val.is_a? ActiveModel::Validations::PresenceValidator }.map(&:attributes).
        flatten.each { |col| output_text << "\n    it { should validate_presence_of :#{col} }" }
      model.validators.select { |val| !val.is_a? ActiveModel::Validations::PresenceValidator }.
        each { |col| output_text << "\n    it \"#{col.class.to_s.demodulize.underscore} test for #{col.attributes.map(&:to_sym).to_s}\"" }
    end << "\n  end"
  end

  def self.associations reflections
    "  context \"associations\" do".tap do |output_text|
      reflections.each_pair { |key, assoc| output_text << "\n    it { should #{translate_assoc assoc.macro} :#{test_assoc_name assoc} }" }
    end << "\n  end"
  end

  def self.methods model
    "".tap do |output_text|
      instance = model.new
      (model.instance_methods(false) - model.columns.map(&:name).map(&:to_sym)).sort.each do |method|
        arity = instance.method(method).arity

        output_text <<
          "  context \"#{method}\" do\n" +
          "    it \"exercises #{method} somehow\" do\n" +
          "      subject.#{method} #{(1..arity).to_a.join(", ")}\n" +
          "    end\n" +
          "  end\n"
      end
    end
  end

  def self.translate_assoc macro
    macro.to_s.gsub(/belongs/, 'belong').gsub(/has/, 'have')
  end

  def self.test_assoc_name assoc
    case assoc.macro
    when /have_many/
      assoc.plural_name
    when /has_one/, /belongs_to/
      assoc.name
    else
      assoc.name
    end
  end

  class ModelDef
    attr_reader :file_name

    def initialize(file_name:)
      @file_name = file_name
    end

    def class_name
      @class_name ||= namespace.map(&:camelcase).join('::').constantize
    end

    private

    def required_file_name
      @required_file_name ||= file_name.sub('app/models/', '')[0..-4]
    end

    def namespace
      @namespace ||= begin
                       parts = required_file_name.split("/")
                       if parts.length > 1
                         parts[0..-1]
                       else
                         parts
                       end
                     end
    end
  end

  def self.require_models
    @model_list ||= [].tap do |model_list|
     Dir.glob('app/models/**/**').each do |file|
        next if File.directory?(file)|| !file.ends_with?('.rb') || file =~ %r{application_record}
        new_def = ModelDef.new(file_name: file)
        model_list << new_def.class_name
      end
    end
  end
end

@fjfish small error:

    def namespace
      @namespace ||= begin
                       parts = required_file_name.split("/")
                       if parts.length > 1
                         parts[0..-1]
                       else
                         parts
                       end
                     end
    end

@jmscholen - thanks - amended.

Hope you found it useful.

IIRC my local copy had to put brackets around the factory stuff, but I haven't needed it for a few days so not checked.