Clarify route encoding test

Since this test changed in 9220935 I noticed that it really doesn't make
sense anymore. I split the tests into 2 groups to explain what each one
does.

First these routes should throw a `bad_request` when the encoding isn't
valid. We're expecting UTF8 encoding and passing binary, that should be
a bad request.

For the second test we are setting the `show` route to set
`self.binary_params_for?` for that route which will convert the
parameters and return a `:ok` instead of a `:bad_request`.

actionpack/test/dispatch/routing_test.rb

@@ -4425,17 +4425,15 @@ class TestInvalidUrls < ActionDispatch::IntegrationTest
     end
   end
 
-  test "invalid UTF-8 encoding is treated as ASCII 8BIT encode" do
+  test "invalid UTF-8 encoding returns a bad request" do
     with_routing do |set|
       set.draw do
         get "/bar/:id", to: redirect("/foo/show/%{id}")
-        get "/foo/show(/:id)", to: "test_invalid_urls/foo#show"
 
         ok = lambda { |env| [200, { "Content-Type" => "text/plain" }, []] }
         get "/foobar/:id", to: ok
 
         ActiveSupport::Deprecation.silence do
-          get "/foo(/:action(/:id))", controller: "test_invalid_urls/foo"
           get "/:controller(/:action(/:id))"
         end
       end
@@ -4446,9 +4444,6 @@ class TestInvalidUrls < ActionDispatch::IntegrationTest
       get "/foo/%E2%EF%BF%BD%A6"
       assert_response :bad_request
 
-      get "/foo/show/%E2%EF%BF%BD%A6"
-      assert_response :ok
-
       get "/bar/%E2%EF%BF%BD%A6"
       assert_response :bad_request
 
@@ -4456,6 +4451,17 @@ class TestInvalidUrls < ActionDispatch::IntegrationTest
       assert_response :bad_request
     end
   end
+
+  test "params encoded with binary_params_for? are treated as ASCII 8bit" do
+    with_routing do |set|
+      set.draw do
+        get "/foo/show(/:id)", to: "test_invalid_urls/foo#show"
+      end
+
+      get "/foo/show/%E2%EF%BF%BD%A6"
+      assert_response :ok
+    end
+  end
 end
 
 class TestOptionalRootSegments < ActionDispatch::IntegrationTest