fix: avoid JSON::ParserError for all server errors

lib/twilio-ruby/http/http_client.rb

@@ -44,8 +44,8 @@ def _request(request)
         @last_response = nil
 
         response = send(request)
-        if response.status == 504
-          object = { message: 'Request timeout', code: 504 }.to_json
+        if (500..599).include?(response.status)
+          object = { message: "Server error (#{response.status})", code: response.status }.to_json
         elsif response.body && !response.body.empty?
           object = response.body
         elsif response.status == 400

spec/http/http_client_spec.rb

@@ -143,19 +143,20 @@
     expect(@client.last_response).to be_nil
   end
 
-  context 'when the response returns a timeout' do
+  context 'when there is a server error' do
+    let(:faraday_connection) { Faraday::Connection.new }
     let(:twilio_response) { @client.request('host', 'port', 'GET', 'url') }
 
     before do
-      faraday_connection = Faraday::Connection.new
-
       allow(Faraday).to receive(:new).and_return(faraday_connection)
-      allow(faraday_connection).to receive(:send).and_return(double('response', status: 504, body: { message: 'any message' }, headers: {}))
     end
 
-    it 'adds a Request timeout message to the response and avoids non-JSON response to raise Json::ParserError' do
-      expect(twilio_response.body).to eq({ 'message' => 'Request timeout', 'code' => 504 })
-      expect(twilio_response.status_code).to eq 504
+    (500..599).each do |status_code|
+      it 'generates a JSON-parseable body' do
+        allow(faraday_connection).to receive(:send).and_return(double('response', status: status_code, body: { message: 'any message' }, headers: {}))
+        expect(twilio_response.body).to eq({ 'message' => "Server error (#{status_code})", 'code' => status_code })
+        expect(twilio_response.status_code).to eq status_code
+      end
     end
   end
 end