QA: Make sure toast is not empty before checking text value

Copies approach for the text of the first heading should be
accounting for the fact that the toast can have an empty
message "" at any given time.

Bug: T170890
Change-Id: Iba8a503a2aea30cb46fba27f000843183e9c46f1

tests/browser/features/step_definitions/common_article_steps.rb

@@ -34,7 +34,12 @@ end
 
 Then(/^I should see a toast with message "(.+)"$/) do |msg|
   step "I should see a toast notification"
-  expect(on(ArticlePage).toast_element.when_present.text).to match msg
+  on(ArticlePage) do |page|
+    page.wait_until do
+      page.toast_element.when_present.text.include? msg
+    end
+    expect(page.toast_element.when_present.text).to match msg
+  end
 end
 
 Then /^I should see a drawer with message "(.+)"$/ do |text|