Resources

attach_file can be used to attach a file to a file input field.
drop can simulate a DragEvent dropping a file on an element
You can also execute Javascript to fake uploads with Uppy and other libraries as needed.

require "application_system_test_case"

class AccountImageTest < ApplicationSystemTestCase
  setup do
    @user = users(:one)
    login_as @user, scope: :user
  end

  test "user can upload new avatar" do
    visit edit_user_registration_path
    attach_file "user[avatar]", file_fixture("avatar.jpg")
    click_button "Update"
    assert_selector "img[src*='avatar.jpg']"
  end

  test "dropzone" do
    visit edit_user_registration_path
    find(".dropzone").drop File.join(file_fixture_path, "avatar.jpg")
  end

  test "uppy" do
    visit edit_user_registration_path
    input = page.driver.evaluate_script Capybara::Selenium::Node::Html5Drag::ATTACH_FILE
    input.set_file file_fixture("avatar.jpg")
    page.driver.execute_script <<~JS, find("#uppy"), input
      var el = arguments[0],
        input = arguments[1],
        file = input.files[0];

      window.uppy.addFile({
        name: file.name,
        type: file.type,
        data: file
      })
    JS
  end