Telegram.bot raises error when there is no default config

lib/telegram/bot/config_methods.rb

@@ -34,7 +34,11 @@ module Telegram
 
       # Default bot.
       def bot
-        @bot ||= bots[:default]
+        @bot ||= bots.fetch(:default) do
+          raise 'Default bot is not configured.' \
+            ' Add :default to bots_config' \
+            ' or use telegram.bot/telegram.bots.default section in secrets.yml.'
+        end
       end
 
       # Hash of botan clients made from #bots.

spec/telegram/bot/config_methods_spec.rb

@@ -22,8 +22,13 @@ RSpec.describe Telegram::Bot::ConfigMethods do
   end
 
   describe '#bot' do
-    subject { registry.bot }
-    it { should eq registry.bots[:default] }
+    subject { -> { registry.bot } }
+    its(:call) { should eq registry.bots[:default] }
+
+    context 'when bot is not configured' do
+      let(:config) { super().except(:default) }
+      it { should raise_error(/bot is not configured/) }
+    end
   end
 
   describe '#bots' do