Better state management in spec and add some tests for MangaDex::Queue

spec/config_spec.cr

@@ -2,11 +2,11 @@ require "./spec_helper"
 
 describe Config do
 	it "creates config if it does not exist" do
-		tempfile = File.tempfile "mango-test-config"
-		config = Config.load tempfile.path
-		File.exists?(tempfile.path).should be_true
-		tempfile.delete
+		with_default_config do |config, logger, path|
+			File.exists?(path).should be_true
+		end
 	end
+
 	it "correctly loads config" do
 		config = Config.load "spec/asset/test-config.yml"
 		config.port.should eq 3000