Added config spec

spec/config_spec.cr

@@ -0,0 +1,20 @@
+require "./spec_helper"
+
+class CustomTestHandler < HTTP::Handler
+  def call(request)
+    call_next request
+  end
+end
+
+describe "Config" do
+  it "sets default port to 3000" do
+    config = Kemal.config
+    config.port.should eq 3000
+  end
+
+  it "adds a custom handler" do
+    config = Kemal.config
+    config.add_handler CustomTestHandler.new
+    config.handlers.size.should eq(1)
+  end
+end