Provide more descriptive error messages when raising exceptions

Before this change the MessageBird::ErrorException always return the
same message in a stacktrace "MessageBird::ErrorException". Now it's
more descriptive and includes the error descriptions received from the
JSON payload.

Author: mcls

lib/messagebird/client.rb

@@ -37,6 +37,8 @@ class ErrorException < StandardError
 
     def initialize(errors)
       @errors = errors
+      message = errors.map { |error| error.message }.join(", ")
+      super(message)
     end
   end
 

lib/messagebird/error.rb

@@ -5,5 +5,13 @@
 module MessageBird
   class Error < MessageBird::Base
     attr_accessor :code, :description, :parameter
+
+    def message
+      if parameter
+        "#{description} (error code: #{code}, parameter: #{parameter})"
+      else
+        "#{description} (error code: #{code})"
+      end
+    end
   end
 end

spec/error_spec.rb

@@ -9,7 +9,7 @@
       .to receive(:request)
       .and_return('{"errors":[{"code": 2,"description": "Request not allowed (incorrect access_key)","parameter": "access_key"}]}')
 
-    expect { client.message('some-id') }.to raise_error(MessageBird::ErrorException)
+    expect { client.message('some-id') }.to raise_error(MessageBird::ErrorException, "Request not allowed (incorrect access_key) (error code: 2, parameter: access_key)")
   end
 
   context 'server responds with an invalid HTTP status code' do
@@ -19,7 +19,7 @@
 
       client = MessageBird::Client.new
 
-      expect { client.message('some-id') }.to raise_error(MessageBird::ServerException)
+      expect { client.message('some-id') }.to raise_error(MessageBird::ServerException, "Unknown response from server")
     end
   end
 end