Add stubbing test helpers for the event bus

core/lib/spree/testing_support/event_helpers.rb

@@ -0,0 +1,103 @@
+# frozen_string_literal: true
+
+require 'spree/event'
+
+module Spree
+  module TestingSupport
+    # RSpec test helpers for the event bus
+    #
+    # If you want to use the methods defined in this module, include it in your
+    # specs:
+    #
+    # @example
+    #   require 'rails_helper'
+    #   require 'spree/testing_support/event_helpers'
+    #
+    #   RSpec.describe MyClass do
+    #     include Spree::TestingSupport::EventHelpers
+    #   end
+    #
+    # or, globally, in your `spec_helper.rb`:
+    #
+    # @example
+    #   require 'spree/testing_support/event_helpers'
+    #
+    #   RSpec.configure do |config|
+    #     config.include Spree::TestingSupport::EventHelpers
+    #   end
+    module EventHelpers
+      extend RSpec::Matchers::DSL
+
+      # Stubs {Spree::Event}
+      #
+      # After you have called this method in an example, {Spree::Event} will no
+      # longer listen to any event for the duration of that example. All the
+      # method invocations on it will be spied but not performed.
+      #
+      # Internally, it stubs {Spree::Event} to a class spy of itself.
+      #
+      # After you call this method, probably you'll want to call some of the
+      # matchers defined in this module.
+      def stub_spree_events
+        stub_const('Spree::Event', class_spy(Spree::Event))
+      end
+
+      # @!method have_been_fired(event_name)
+      #   Matcher to test that an event has been fired via {Spree::Event#fire}
+      #
+      #   Before using this matcher, you need to call {#stub_spree_events}.
+      #
+      #   Remember that the event listeners won't be performed.
+      #
+      #   @example
+      #     it 'fires foo event' do
+      #       stub_spree_events
+      #
+      #       Spree::Event.fire 'foo'
+      #
+      #       expect('foo').to have_been_fired
+      #     end
+      #
+      #   It can be chain through `with` to match with the published payload:
+      #
+      #   @example
+      #     it 'fires foo event with the expected payload' do
+      #       stub_spree_events
+      #
+      #       Spree::Event.fire 'foo', bar: :baz, qux: :quux
+      #
+      #       expect('foo').to have_been_fired.with(a_hash_including(bar: :baz))
+      #     end
+      #
+      #   @param [String, Symbol] event_name
+      matcher :have_been_fired do
+        chain :with, :payload
+
+        match do |expected_event|
+          expected_event = normalize_name(expected_event)
+          arguments = payload ? [expected_event, payload] : [expected_event, any_args]
+          expect(Spree::Event).to have_received(:fire).with(*arguments)
+        end
+
+        failure_message do |expected_event|
+          <<~MSG
+            expected #{expected_event.inspect} to have been fired.
+            Make sure that provided payload, if any, also matches.
+          MSG
+        end
+
+        def normalize_name(event_name)
+          if event_name.is_a?(String)
+            eq(event_name).or(eq(event_name.to_sym))
+          elsif event_name.is_a?(Symbol)
+            eq(event_name).or(eq(event_name.to_s))
+          else
+            raise ArgumentError, <<~MSG
+              "#{event_name.inspect} is not a valid event name. It must be a String or a Symbol."
+            MSG
+          end
+        end
+      end
+    end
+  end
+end

core/spec/lib/spree/core/testing_support/event_helpers_spec.rb

@@ -0,0 +1,110 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'spree/testing_support/event_helpers'
+
+RSpec.describe Spree::TestingSupport::EventHelpers do
+  include described_class
+
+  describe '#stub_spree_events' do
+    it 'creates a spy class from Spree::Event and assigns to itself' do
+      stub_spree_events
+
+      expect(Spree::Event.inspect).to include('ClassDouble')
+
+      Spree::Event.fire 'foo'
+
+      expect(Spree::Event).to have_received(:fire)
+    end
+  end
+
+  describe '#have_been_fired' do
+    it "matches when the event has been fired without payload and there's no expectation on it" do
+      stub_spree_events
+
+      Spree::Event.fire 'foo'
+
+      expect('foo').to have_been_fired
+    end
+
+    it "matches when the event has been fired with payload but there's no expectation on it" do
+      stub_spree_events
+
+      Spree::Event.fire 'foo', bar: :baz
+
+      expect('foo').to have_been_fired
+    end
+
+    it "matches when the event has been fired with payload and the expectation on it matches" do
+      stub_spree_events
+
+      Spree::Event.fire 'foo', bar: :baz
+
+      expect('foo').to have_been_fired.with(bar: :baz)
+    end
+
+    it "matches when fired as string and matched as string" do
+      stub_spree_events
+
+      Spree::Event.fire 'foo'
+
+      expect('foo').to have_been_fired
+    end
+
+    it "matches when fired as string but matched as symbol" do
+      stub_spree_events
+
+      Spree::Event.fire 'foo'
+
+      expect(:foo).to have_been_fired
+    end
+
+    it "matches when fired as symbol but matched as string" do
+      stub_spree_events
+
+      Spree::Event.fire :foo
+
+      expect('foo').to have_been_fired
+    end
+
+    it "matches when fired as symbol and matched as symbol" do
+      stub_spree_events
+
+      Spree::Event.fire :foo
+
+      expect(:foo).to have_been_fired
+    end
+
+    it "can match payload with an inner matcher" do
+      stub_spree_events
+
+      Spree::Event.fire 'foo', bar: :baz, tar: :tar
+
+      expect('foo').to have_been_fired.with(a_hash_including(bar: :baz))
+    end
+
+    it "doesn't match when the event hasn't been fired" do
+      stub_spree_events
+
+      expect {
+        expect('foo').to have_been_fired
+      }.to raise_error /expected "foo" to have been fired/
+    end
+
+    it "doesn't match when the event has been fired but the payload doesn't match" do
+      stub_spree_events
+
+      Spree::Event.fire 'foo', foo: :bar
+
+      expect {
+        expect('foo').to have_been_fired.with(bar: :baz)
+      }.to raise_error /Make sure that provided payload.*also matches/
+    end
+
+    it "raises when expected event is not a valid name" do
+      expect {
+        expect([]).to have_been_fired.with(bar: :baz)
+      }.to raise_error /not a valid event name/
+    end
+  end
+end