Support selecting multiple cards by using a list of numbers (separated by comma, or space)

https://3.basecamp.com/2914079/buckets/37331921/todos/8620236700#__recording_8620273944

test/models/command/filter_cards_test.rb

@@ -0,0 +1,21 @@
+require "test_helper"
+
+class Command::FilterCardsTest < ActionDispatch::IntegrationTest
+  include CommandTestHelper
+
+  setup do
+    @card_ids = cards(:logo, :layout).collect(&:id)
+  end
+
+  test "redirects to the cards index filtering by cards" do
+    result = execute_command "#{@card_ids.join(" ")}"
+
+    assert_equal cards_path(indexed_by: "newest", card_ids: @card_ids), result.url
+  end
+
+  test "respects existing filters" do
+    result = execute_command "#{@card_ids.join(",")}", context_url: "http://37signals.fizzy.localhost:3006/cards?collection_ids%5B%5D=#{collections(:writebook).id}"
+
+    assert_equal cards_path(indexed_by: "newest", collection_ids: [ collections(:writebook).id ], card_ids: @card_ids), result.url
+  end
+end