ActionController::RoutingErrorが解決できない

現在、RailsのオリジナルアプリにBootstrapを導入したのですが、RspecにてActionController::RoutingError:No route matches [GET] "/custom.css"が発生し解決できず、困っております。

custom.cssというファイルは存在しておらず、Bootstrapを導入時に新規でcustom.scssを作成しております。

また、application.scssに*= require custom.cssを追記しても改善されませんでした。

何卒、よろしくお願いいたします。

エラーメッセージ

 Failure/Error: raise ActionController::RoutingError, "No route matches [#{env['REQUEST_METHOD']}] #{env['PATH_INFO'].inspect}"
     
     ActionController::RoutingError:
       No route matches [GET] "/custom.css"
     
     [Screenshot]: /Users/hogehoge/Portfolio/connect/tmp/screenshots/failures_r_spec_example_groups_static_pages_top_nested_投稿を削除後、削除成功のフラッシュが表示されること_9.png

 # /Users/hogehoge/Portfolio/connect/vendor/bundle/ruby/2.6.0/gems/actionpack-6.0.3.4/lib/action_dispatch/middleware/debug_exceptions.rb:36:in `call'
     # /Users/hogehoge/Portfolio/connect/vendor/bundle/ruby/2.6.0/gems/actionpack-6.0.3.4/lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
 
Showing full backtrace because every line was filtered out.
     #   See docs for RSpec::Configuration#backtrace_exclusion_patterns and
     #   RSpec::Configuration#backtrace_inclusion_patterns for more information.
     # ------------------
     # --- Caused by: ---
     # Capybara::CapybaraError:
     #   Your application server raised an error - It has been raised in your test code because Capybara.raise_server_errors == true
     #   ./spec/support/test_helper.rb:13:in `login_for_system'

application.scss

/*
* require_tree .
* require_self
*= require animate.css
*= require icomoon.css
*= require bootstrap.css
*= require flexslider.css
*= require style.css
*= require magnific-popup.css
*/
@import "style.scss";
@import "bootstrap-sprockets";
@import "bootstrap.scss";
@import "custom.scss";
@import "icomoon/style";