[chore] add spec for LinkExistingWikiPageForm

Covers the hidden link attributes and the wiki page selection tree.

modules/wikis/spec/forms/wikis/link_existing_wiki_page_form_spec.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe Wikis::LinkExistingWikiPageForm, type: :forms do
+  include Rails.application.routes.url_helpers
+
+  include_context "with rendered form"
+
+  let(:model) { build_stubbed(:relation_wiki_page_link) }
+
+  it "renders the link attributes as hidden fields", :aggregate_failures do
+    expect(page).to have_field("wikis_relation_page_link[provider_id]", type: :hidden, with: model.provider_id)
+    expect(page).to have_field("wikis_relation_page_link[linkable_type]", type: :hidden, with: model.linkable_type)
+    expect(page).to have_field("wikis_relation_page_link[linkable_id]", type: :hidden, with: model.linkable_id)
+  end
+
+  it "renders the wiki page selection", :aggregate_failures do
+    expect(page).to have_selector :fieldset, "Wiki page"
+    expect(page).to have_element :"filterable-tree-view",
+                                 src: search_wiki_pages_path(provider_id: model.provider_id,
+                                                             name: "wiki_page_selection")
+    expect(page).to have_field "Filter", type: :search, placeholder: "Search for a wiki page"
+  end
+end