Feature: Add Rails generator and rake task support for creating data migration test coverage

README.md

@@ -83,6 +83,7 @@ You can generate a data migration as you would a schema migration:
     rake data:migrate:up                           # Runs the "up" for a given migration VERSION
     rake data:rollback                             # Rolls the schema back to the previous version (specify steps w/ STEP=n)
     rake data:schema:load                          # Load data_schema.rb file into the database without running the data migrations
+    rake data:tests:setup                          # Setup data migrations for identified test suite
     rake data:version                              # Retrieves the current schema version number for data migrations
     rake db:abort_if_pending_migrations:with_data  # Raises an error if there are pending migrations or data migrations
     rake db:forward:with_data                      # Pushes the schema to the next version (specify steps w/ STEP=n)
@@ -125,10 +126,24 @@ DataMigrate.configure do |config|
     'password' => nil,
   }
   config.spec_name = 'primary'
-end
 
+  # Enable data_migration generator to create test files
+  config.test_support_enabled = true
+end
 ```
 
+### Test Suite Support
+
+When `config.test_support_enabled = true`, the `data_migration` generator will create test files for your data migrations. This is dependent on
+the test suite you are using.
+
+For example, if you run `rails g data_migration add_this_to_that`, the following files will be created:
+
+- `/spec/db/data/add_this_to_that_spec.rb` (for RSpec)
+- `/test/db/data/add_this_to_that_test.rb` (for Minitest)
+
+You can also run the Rake task `rake data:tests:setup` to configure your test suite to load data migrations.
+
 ## Capistrano Support
 
 The gem comes with a capistrano task that can be used instead of `capistrano/rails/migrations`.

lib/data_migrate.rb

@@ -9,7 +9,9 @@
 require File.join(File.dirname(__FILE__), "data_migrate", "status_service")
 require File.join(File.dirname(__FILE__), "data_migrate", "migration_context")
 require File.join(File.dirname(__FILE__), "data_migrate", "railtie")
+require File.join(File.dirname(__FILE__), "data_migrate", "helpers/infer_test_suite_type")
 require File.join(File.dirname(__FILE__), "data_migrate", "tasks/data_migrate_tasks")
+require File.join(File.dirname(__FILE__), "data_migrate", "tasks/setup_tests")
 require File.join(File.dirname(__FILE__), "data_migrate", "config")
 require File.join(File.dirname(__FILE__), "data_migrate", "schema_migration")
 require File.join(File.dirname(__FILE__), "data_migrate", "database_configurations_wrapper")

lib/data_migrate/config.rb

@@ -1,7 +1,7 @@
 module DataMigrate
   include ActiveSupport::Configurable
-  class << self
 
+  class << self
     def configure
       yield config
     end
@@ -12,7 +12,7 @@ def config
   end
 
   class Config
-    attr_accessor :data_migrations_path, :data_template_path, :db_configuration, :spec_name
+    attr_accessor :data_migrations_path, :data_template_path, :db_configuration, :spec_name, :test_support_enabled
 
     DEFAULT_DATA_TEMPLATE_PATH = "data_migration.rb"
 
@@ -21,6 +21,7 @@ def initialize
       @data_template_path = DEFAULT_DATA_TEMPLATE_PATH
       @db_configuration = nil
       @spec_name = nil
+      @test_support_enabled = false
     end
 
     def data_template_path=(value)

lib/data_migrate/helpers/infer_test_suite_type.rb

@@ -0,0 +1,15 @@
+module DataMigrate
+  module Helpers
+    class InferTestSuiteType
+      def call
+        if File.exist?(Rails.root.join('spec', 'spec_helper.rb'))
+          :rspec
+        elsif File.exist?(Rails.root.join('test', 'test_helper.rb'))
+          :minitest
+        else
+          raise StandardError.new('Unable to determine test suite')
+        end
+      end
+    end
+  end
+end

lib/data_migrate/tasks/setup_tests.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module DataMigrate
+  module Tasks
+    class SetupTests
+      INJECTION_MATCHER = Regexp.new(/require_relative ["|']\.\.\/config\/environment["|']/)
+
+      def call
+        return if injection_exists?
+
+        if find_injection_location.nil?
+          puts 'data_migrate: config/environment.rb was not found in the test helper file.'
+          return
+        end
+
+        add_newline
+
+        lines_for_injection.reverse.each do |line|
+          file_contents.insert(find_injection_location, "#{line}\n")
+        end
+
+        add_newline
+
+        File.open(test_helper_file_path, 'w') do |file|
+          file.puts file_contents
+        end
+
+        puts 'data_migrate: Test setup complete.'
+      end
+
+      private
+
+      def test_helper_file_path
+        case DataMigrate::Helpers::InferTestSuiteType.new.call
+        when :rspec
+          Rails.root.join('spec', 'rails_helper.rb')
+        when :minitest
+          Rails.root.join('test', 'test_helper.rb')
+        end
+      end
+
+      def file_contents
+        @_file_contents ||= File.readlines(test_helper_file_path)
+      end
+
+      def find_injection_location
+        @_find_injection_location ||= begin
+          index = file_contents.index { |line| line.match?(INJECTION_MATCHER) }
+          index.present? ? index + 1 : nil
+        end
+      end
+
+      def add_newline
+        file_contents.insert(find_injection_location, "\n")
+      end
+
+      def lines_for_injection
+        [
+          "# data_migrate: Include data migrations for writing test coverage",
+          "Dir[Rails.root.join(DataMigrate.config.data_migrations_path, '*.rb')].each { |f| require f }"
+        ]
+      end
+
+      def injection_exists?
+        file_contents.each_cons(lines_for_injection.length) do |content_window|
+          if content_window.map(&:strip) == lines_for_injection.map(&:strip)
+            puts 'data_migrate: Test setup already exists.'
+            return true
+          end
+        end
+
+        false
+      end
+    end
+  end
+end

lib/generators/data_migration/data_migration_generator.rb

@@ -15,10 +15,30 @@ class DataMigrationGenerator < Rails::Generators::NamedBase
       def create_data_migration
         set_local_assigns!
         migration_template template_path, data_migrations_file_path
+        create_data_migration_test
       end
 
       protected
 
+      def create_data_migration_test
+        return unless DataMigrate.config.test_support_enabled
+
+        case DataMigrate::Helpers::InferTestSuiteType.new.call
+        when :rspec
+          template "data_migration_spec.rb", data_migrations_spec_file_path
+        when :minitest
+          template "data_migration_test.rb", data_migrations_test_file_path
+        end
+      end
+
+      def data_migrations_test_file_path
+        File.join(Rails.root, 'test', DataMigrate.config.data_migrations_path, "#{file_name}_test.rb")
+      end
+
+      def data_migrations_spec_file_path
+        File.join(Rails.root, 'spec', DataMigrate.config.data_migrations_path, "#{file_name}_spec.rb")
+      end
+
       def set_local_assigns!
         if file_name =~ /^(add|remove)_.*_(?:to|from)_(.*)/
           @migration_action = $1

lib/generators/data_migration/templates/data_migration_spec.rb

@@ -0,0 +1,9 @@
+require 'rails_helper'
+
+describe <%= migration_class_name %>, type: :data_migration do
+  let(:migration) { <%= migration_class_name %>.new }
+
+  pending "should test `migration.up`"
+
+  pending "should test `migration.down`"
+end

lib/generators/data_migration/templates/data_migration_test.rb

@@ -0,0 +1,15 @@
+require 'test_helper'
+
+class <%= migration_class_name %>Test < ActiveSupport::TestCase
+  def setup
+    @migration = <%= migration_class_name %>.new
+  end
+
+  def test_migration_up
+    skip("Pending test coverage for @migration.up")
+  end
+
+  def test_migration_down
+    skip("Pending test coverage for @migration.down")
+  end
+end

spec/data_migrate/helpers/infer_test_suite_type_spec.rb

@@ -0,0 +1,44 @@
+require 'spec_helper'
+
+describe DataMigrate::Helpers::InferTestSuiteType do
+  subject(:infer_test_suite) { described_class.new }
+
+  describe '#call' do
+    before do
+      allow(Rails).to receive(:root).and_return(Pathname.new('/fake/path'))
+    end
+
+    context 'when RSpec is detected' do
+      before do
+        allow(File).to receive(:exist?).with(Rails.root.join('spec', 'spec_helper.rb')).and_return(true)
+        allow(File).to receive(:exist?).with(Rails.root.join('test', 'test_helper.rb')).and_return(false)
+      end
+
+      it 'returns :rspec' do
+        expect(infer_test_suite.call).to eq(:rspec)
+      end
+    end
+
+    context 'when Minitest is detected' do
+      before do
+        allow(File).to receive(:exist?).with(Rails.root.join('spec', 'spec_helper.rb')).and_return(false)
+        allow(File).to receive(:exist?).with(Rails.root.join('test', 'test_helper.rb')).and_return(true)
+      end
+
+      it 'returns :minitest' do
+        expect(infer_test_suite.call).to eq(:minitest)
+      end
+    end
+
+    context 'when no test suite is detected' do
+      before do
+        allow(File).to receive(:exist?).with(Rails.root.join('spec', 'spec_helper.rb')).and_return(false)
+        allow(File).to receive(:exist?).with(Rails.root.join('test', 'test_helper.rb')).and_return(false)
+      end
+
+      it 'raises an error' do
+        expect { infer_test_suite.call }.to raise_error(StandardError, 'Unable to determine test suite')
+      end
+    end
+  end
+end

spec/data_migrate/tasks/setup_tests_spec.rb

@@ -0,0 +1,93 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe DataMigrate::Tasks::SetupTests do
+  let(:file_contents_with_injection) do
+    <<~FILE_CONTENTS
+      # This file is copied to spec/ when you run 'rails generate rspec:install'
+      require 'spec_helper'
+      ENV['RAILS_ENV'] ||= 'test'
+      require_relative '../config/environment'
+
+      # data_migrate: Include data migrations for writing test coverage
+      Dir[Rails.root.join(DataMigrate.config.data_migrations_path, '*.rb')].each { |f| require f }
+    FILE_CONTENTS
+  end
+  let(:file_contents_without_injection) do
+    <<~FILE_CONTENTS
+      # This file is copied to spec/ when you run 'rails generate rspec:install'
+      require 'spec_helper'
+      ENV['RAILS_ENV'] ||= 'test'
+      require_relative '../config/environment'
+    FILE_CONTENTS
+  end
+  let(:file_contents_without_injection_matcher) do
+    <<~FILE_CONTENTS
+      # This file is copied to spec/ when you run 'rails generate rspec:install'
+      require 'spec_helper'
+      ENV['RAILS_ENV'] ||= 'test'
+    FILE_CONTENTS
+  end
+  let(:rails_root) { Pathname.new('/fake/app') }
+  let(:test_suite_inferrer) { instance_double(DataMigrate::Helpers::InferTestSuiteType) }
+
+  before do
+    allow(Rails).to receive(:root).and_return(rails_root)
+    allow(DataMigrate::Helpers::InferTestSuiteType).to receive(:new).and_return(test_suite_inferrer)
+  end
+
+  describe "#call" do
+    context 'when the injected code already exists' do
+      it 'returns early' do
+        allow(test_suite_inferrer).to receive(:call).and_return(:rspec)
+        allow(File).to receive(:readlines).and_return(file_contents_with_injection.lines)
+
+        expect(File).not_to receive(:open)
+
+        expect {
+          DataMigrate::Tasks::SetupTests.new.call
+        }.to output(/data_migrate: Test setup already exists./).to_stdout
+      end
+
+      context 'when the INJECTION_MATCHER is not found' do
+        it 'returns early' do
+          allow(test_suite_inferrer).to receive(:call).and_return(:rspec)
+          allow(File).to receive(:readlines).and_return(file_contents_without_injection_matcher.lines)
+
+          expect(File).not_to receive(:open)
+
+          expect {
+            DataMigrate::Tasks::SetupTests.new.call
+          }.to output(/data_migrate: config\/environment.rb was not found in the test helper file./).to_stdout
+        end
+      end
+
+      context 'for RSpec' do
+        it 'calls File.open for writing to rails_helper.rb' do
+          allow(test_suite_inferrer).to receive(:call).and_return(:rspec)
+          allow(File).to receive(:readlines).and_return(file_contents_without_injection.lines)
+
+          expect(File).to receive(:open).with(rails_root.join('spec', 'rails_helper.rb'), 'w')
+
+          expect {
+            DataMigrate::Tasks::SetupTests.new.call
+          }.to output(/data_migrate: Test setup complete./).to_stdout
+        end
+      end
+
+      context 'for Minitest' do
+        it 'calls File.open for writing to test_helper.rb' do
+          allow(test_suite_inferrer).to receive(:call).and_return(:minitest)
+          allow(File).to receive(:readlines).and_return(file_contents_without_injection.lines)
+
+          expect(File).to receive(:open).with(rails_root.join('test', 'test_helper.rb'), 'w')
+
+          expect {
+            DataMigrate::Tasks::SetupTests.new.call
+          }.to output(/data_migrate: Test setup complete./).to_stdout
+        end
+      end
+    end
+  end
+end