Fix customization of budget_execution_no_image

We forgot to change the line rendering the image in commits 3574bf867c
and 810bdae37a, and so the custom image was being ignored.

Note that, in the test, we're stubbing a constant instead of adding a
new image. The main reason is that, if we add a new image, forks would
have to change the image when they change the `VALID_IMAGES` constant;
otherwise the tests would fail.

app/components/budgets/executions/image_component.html.erb

@@ -3,5 +3,5 @@
 <% elsif investment.image.present? %>
   <%= image_tag investment.image.variant(:large), alt: investment.image.title %>
 <% else %>
-  <%= image_tag "budget_execution_no_image.jpg", alt: investment.title %>
+  <%= image_tag image_path_for("budget_execution_no_image.jpg"), alt: investment.title %>
 <% end %>

app/components/budgets/executions/image_component.rb

@@ -1,5 +1,6 @@
 class Budgets::Executions::ImageComponent < ApplicationComponent
   attr_reader :investment
+  delegate :image_path_for, to: :helpers
 
   def initialize(investment)
     @investment = investment

spec/components/budgets/executions/image_component_spec.rb

@@ -0,0 +1,25 @@
+require "rails_helper"
+
+describe Budgets::Executions::ImageComponent do
+  context "investment and milestone without image" do
+    let(:component) { Budgets::Executions::ImageComponent.new(Budget::Investment.new) }
+
+    it "shows the default image" do
+      render_inline component
+
+      expect(page).to have_css "img[src*='budget_execution_no_image']"
+    end
+
+    it "shows a custom default image when available" do
+      stub_const("#{SiteCustomization::Image}::VALID_IMAGES", { "budget_execution_no_image" => [260, 80] })
+      create(:site_customization_image,
+             name: "budget_execution_no_image",
+             image: fixture_file_upload("logo_header-260x80.png"))
+
+      render_inline component
+
+      expect(page).to have_css "img[src$='logo_header-260x80.png']"
+      expect(page).not_to have_css "img[src*='budget_execution_no_image']"
+    end
+  end
+end