Constrain the ChapterController catch-all route to slug format

config/routes.rb

@@ -201,7 +201,7 @@
   get 'donate' => 'pages#show', id: 'donate'
   get 'codebar-stories-podcast' => 'pages#show', id: 'codebar-stories-podcast'
 
-  get ':id' => 'chapter#show', as: :chapter
+  get ':id' => 'chapter#show', as: :chapter, format: false, constraints: { id: /[a-z0-9_-]+/ }
 
   # Redirects
   get '/my/jobs/new', to: redirect('https://jobs.codebar.io/my/jobs/new')

spec/routing/chapter_routing_spec.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'chapter catch-all route' do
+  it 'routes a chapter slug to chapter#show' do
+    expect(get: '/london').to route_to(controller: 'chapter', action: 'show', id: 'london')
+  end
+
+  # Chapter#set_slug builds slugs with name.parameterize, which produces
+  # lowercase letters, digits, hyphens, and underscores.
+  it 'routes every character class the slug generator can produce' do
+    expect(get: '/123').to route_to(controller: 'chapter', action: 'show', id: '123')
+    expect(get: '/south-london').to route_to(controller: 'chapter', action: 'show', id: 'south-london')
+    expect(get: '/spring_wildcats').to route_to(controller: 'chapter', action: 'show', id: 'spring_wildcats')
+  end
+
+  it 'does not route paths containing dots' do
+    expect(get: '/key.pem').not_to be_routable
+  end
+
+  it 'does not route paths containing uppercase characters' do
+    expect(get: '/Shanghai').not_to be_routable
+  end
+end