rails--rails/activerecord/test/cases/transaction_isolation_test.rb

require 'cases/helper'

unless ActiveRecord::Base.connection.supports_transaction_isolation?
  class TransactionIsolationUnsupportedTest < ActiveRecord::TestCase
    self.use_transactional_fixtures = false

    class Tag < ActiveRecord::Base
    end

    test "setting the isolation level raises an error" do
      assert_raises(ActiveRecord::TransactionIsolationError) do
        Tag.transaction(isolation: :serializable) { }
      end
    end
  end
end

if ActiveRecord::Base.connection.supports_transaction_isolation?
  class TransactionIsolationTest < ActiveRecord::TestCase
    self.use_transactional_fixtures = false

    class Tag < ActiveRecord::Base
      self.table_name = 'tags'
    end

    class Tag2 < ActiveRecord::Base
      self.table_name = 'tags'
    end

    setup do
      Tag.establish_connection :arunit
      Tag2.establish_connection :arunit
      Tag.destroy_all
    end

    # It is impossible to properly test read uncommitted. The SQL standard only
    # specifies what must not happen at a certain level, not what must happen. At
    # the read uncommitted level, there is nothing that must not happen.
    if ActiveRecord::Base.connection.transaction_isolation_levels.include?(:read_uncommitted)
      test "read uncommitted" do
        Tag.transaction(isolation: :read_uncommitted) do
          assert_equal 0, Tag.count
          Tag2.create
          assert_equal 1, Tag.count
        end
      end
    end

    # We are testing that a dirty read does not happen
    test "read committed" do
      Tag.transaction(isolation: :read_committed) do
        assert_equal 0, Tag.count

        Tag2.transaction do
          Tag2.create
          assert_equal 0, Tag.count
        end
      end

      assert_equal 1, Tag.count
    end

    # We are testing that a nonrepeatable read does not happen
    if ActiveRecord::Base.connection.transaction_isolation_levels.include?(:repeatable_read)
      test "repeatable read" do
        tag = Tag.create(name: 'jon')

        Tag.transaction(isolation: :repeatable_read) do
          tag.reload
          Tag2.find(tag.id).update(name: 'emily')

          tag.reload
          assert_equal 'jon', tag.name
        end

        tag.reload
        assert_equal 'emily', tag.name
      end
    end

    # We are only testing that there are no errors because it's too hard to
    # test serializable. Databases behave differently to enforce the serializability
    # constraint.
    test "serializable" do
      Tag.transaction(isolation: :serializable) do
        Tag.create
      end
    end

    test "setting isolation when joining a transaction raises an error" do
      Tag.transaction do
        assert_raises(ActiveRecord::TransactionIsolationError) do
          Tag.transaction(isolation: :serializable) { }
        end
      end
    end

    test "setting isolation when starting a nested transaction raises error" do
      Tag.transaction do
        assert_raises(ActiveRecord::TransactionIsolationError) do
          Tag.transaction(requires_new: true, isolation: :serializable) { }
        end
      end
    end
  end
end