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Creating Long-Lived Web Apps with Ruby on Rails

Fully Implement and Test Business Logic

Explore how to fully implement and test business logic within a Ruby on Rails app by focusing on validation, mailer integration, and test-first workflow. Understand the importance of testing real-world scenarios involving widget status, pricing, and email notifications to ensure reliable, maintainable code.

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Testing the business logic

With our seam now defined, we find it easier to switch to a test-first workflow. The logic we have to build is pretty complex, and this will require a lot of tests.

  • Create a valid widget for a manufacturer created three months ago. Check that the status is “Fresh” and that no emails were sent.
  • Create a valid widget with a price of $7,500.01 and make sure the finance staff was emailed.
  • Create a valid widget with a manufacturer created 59 days ago and make sure the administrative staff was emailed.
  • Create invalid widgets and check the errors. For these cases, we don’t need to have one test for every single validation, though each does need testing:
    • Widgets missing a name, price, and manufacturer.
    • Widget with a four-character name.
    • Widget for an old manufacturer with a price of $99.
    • Widget with a price over $10,000.
    • Widget with a price of $0.

For the sake of brevity, we won’t implement all of these, but we will implement a few that allow us to see the effect of Rails validations and mailers on our implementation and tests.

Let’s start with the basic happy path.

Ruby
# test/services/widget_creator_test.rb
require "test_helper"
class WidgetCreatorTest < ActiveSupport::TestCase
  setup do
    @widget_creator = WidgetCreator.new
    @manufacturer = FactoryBot.create(:manufacturer,
                                      created_at: 1.year.ago)
    FactoryBot.create(:widget_status)
  end
  test "widgets have a default status of 'Fresh'" do
    result = @widget_creator.create_widget(Widget.new(
      name: "Stembolt",
      price_cents: 1_000_00,
      manufacturer_id: @manufacturer.id
    ))
    assert result.created?
    assert_equal Widget.first, result.widget
    assert_equal "Fresh",result.widget.widget_status.name
  end
end

This test should fail because we’re using whatever status is returned by WidgetStatus.first and not looking for one named “Fresh”.

Shell
 bin/rails test test/services/widget_creator_test.rb || echo  \
 Test Failed
Running 1 tests in a single process (parallelization thresho…
Run options: --seed 19750
# Running:
Failure:
WidgetCreatorTest#test_widgets_have_a_default_status_of_'Fre…
Expected: "Fresh"
  Actual: "maiores"
rails test test/services/widget_creator_test.rb:10
Finished in 0.405940s, 2.4634 runs/s, 7.3902 assertions/s.
1 runs, 3 assertions, 1 failures, 0 errors, 0 skips
Test Failed

We could fix this by naming the status we’re ...