DEV: Add system tests (#31)

Why does this commit do?

This commit improves the test coverage for the theme by adding system
tests which covers the basic functionality of the theme.

spec/system/viewing_brand_header_spec.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+RSpec.describe "Viewing the brand header", type: :system do
+  let(:theme) { upload_theme_component }
+
+  it "respects the `show_bar_on_mobile setting` when displaying the brand header on mobile",
+     mobile: true do
+    theme.update_setting(:show_bar_on_mobile, true)
+    theme.save!
+
+    visit("/")
+
+    expect(page).to have_css(".b-header")
+
+    theme.update_setting(:show_bar_on_mobile, false)
+    theme.save!
+
+    visit("/")
+
+    expect(page).not_to have_css(".b-header")
+  end
+
+  it "should display the brand header with the correct title and links" do
+    theme.update_setting(:website_url, "http://some.url.com")
+    theme.update_setting(:brand_name, "some name")
+    theme.update_setting(:logo_url, "http://some.url.com/logo.png")
+
+    theme.update_setting(
+      :links,
+      "First Link,http://some.url.com/first|Second Link,http://some.url.com/second,_blank",
+    )
+
+    theme.update_setting(
+      :icons,
+      "wrench,http://some.url.com/some-wrench-link|pencil,http://some.url.com/some-pencil-link,_blank",
+    )
+    theme.save!
+
+    visit("/")
+
+    expect(page).to have_link(nil, href: "http://some.url.com")
+
+    expect(page).to have_selector(
+      'img#brand-logo[title="some name"][src="http://some.url.com/logo.png"]',
+    )
+
+    expect(page).to have_link("First Link", href: "http://some.url.com/first")
+    expect(page).to have_link("Second Link", href: "http://some.url.com/second", target: "_blank")
+
+    expect(page).to have_selector('a[href="http://some.url.com/some-wrench-link"] .d-icon-wrench')
+
+    expect(page).to have_selector(
+      'a[href="http://some.url.com/some-pencil-link"][target="_blank"] .d-icon-pencil',
+    )
+  end
+end