Extract component for balloting budget admin stats

We're also moving the tests, but we're keeping one system test in order
to test the controller and the navigation to get to this page.

Note we're slightly changing the order of the methods in the component;
the order of the instance variables was `user_`, `vote_`, `vote_`,
`user_`, which was hard to follow.

spec/components/admin/stats/budget_balloting_component_spec.rb

@@ -0,0 +1,28 @@
+require "rails_helper"
+
+describe Admin::Stats::BudgetBallotingComponent do
+  let(:budget) { create(:budget, :balloting) }
+  let(:heading) { create(:budget_heading, budget: budget) }
+  let(:investment) { create(:budget_investment, :feasible, :selected, heading: heading) }
+
+  it "shows the number of votes in investment projects" do
+    investment_2 = create(:budget_investment, :feasible, :selected, budget: budget)
+
+    create(:user, ballot_lines: [investment, investment_2])
+    create(:user, ballot_lines: [investment_2])
+
+    render_inline Admin::Stats::BudgetBallotingComponent.new(budget)
+
+    expect(page).to have_css "p", exact_text: "Votes 3", normalize_ws: true
+  end
+
+  it "shows the number of users that have voted a investment project" do
+    create(:user, ballot_lines: [investment])
+    create(:user, ballot_lines: [investment])
+    create(:user)
+
+    render_inline Admin::Stats::BudgetBallotingComponent.new(budget)
+
+    expect(page).to have_css "p", exact_text: "Participants 2", normalize_ws: true
+  end
+end