DEV: Move discourse-chat to the core repo. (#18776)

As part of this move, we are also renaming `discourse-chat` to `chat`.

plugins/chat/spec/support/examples/chatable_model.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+RSpec.shared_examples "a chatable model" do
+  describe "#chat_channel" do
+    subject(:chat_channel) { chatable.chat_channel }
+
+    it "returns a new chat channel model" do
+      expect(chat_channel).to have_attributes persisted?: false,
+                                              class: channel_class,
+                                              chatable: chatable
+    end
+  end
+
+  describe "#create_chat_channel!" do
+    subject(:create_chat_channel) { chatable.create_chat_channel!(name: name) }
+
+    let(:name) { "a custom name" }
+
+    it "creates a proper chat channel" do
+      expect { create_chat_channel }.to change { channel_class.count }.by(1)
+      expect(channel_class.last).to have_attributes chatable: chatable, name: name
+    end
+  end
+end