Improve QA sanity selectors test output message

qa/qa/page/base.rb

@@ -50,7 +50,7 @@ module QA
 
       def self.errors
         if views.empty?
-          return ["#{name} class does not have views / elements defined!"]
+          return ["Page class does not have views / elements defined!"]
         end
 
         views.map(&:errors).flatten

qa/qa/page/element.rb

@@ -19,6 +19,10 @@ module QA
       def matches?(line)
         !!(line =~ expression)
       end
+
+      def to_s
+        @name
+      end
     end
   end
 end

qa/qa/page/validator.rb

@@ -2,7 +2,12 @@ module QA
   module Page
     class Validator
       ValidationError = Class.new(StandardError)
-      Error = Struct.new(:page, :message)
+
+      Error = Struct.new(:page, :message) do
+        def to_s
+          "Error: #{page} - #{message}"
+        end
+      end
 
       def initialize(constant)
         @module = constant

qa/qa/scenario/test/sanity/selectors.rb

@@ -13,6 +13,34 @@ module QA
             end
 
             validators.map(&:errors).flatten.tap do |errors|
+              break if errors.none?
+
+              STDERR.puts <<~EOS
+                GitLab QA sanity selectors validation test detected problems
+                your merge request!
+
+                The purpose of this tes is to make sure that GitLab QA tests,
+                that are entirely black-box and click-driven scenario, do match
+                pages structure / layout in the GitLab CE / EE repositories.
+
+                It looks like you have changed views / pages / selectors, and
+                these are now out of sync with what we have defined in `qa/`
+                directory.
+
+                Please update code in `qa/` directory to match currect changes
+                in this merge request.
+
+                For more help see documentation in `qa/page/README.md` file or
+                ask for help on #qa channel on Slack (GitLab Team only).
+
+                If you are not a team member, and you still need help to
+                contribute, please open an issue in GitLab QA issue tracker.
+
+                Please see errors described below.
+
+              EOS
+
+              STDERR.puts errors
             end
 
             validators.each(&:validate!)

qa/spec/page/base_spec.rb

@@ -56,7 +56,7 @@ describe QA::Page::Base do
 
       it 'appends an error about missing views / elements block' do
         expect(described_class.errors)
-          .to include 'QA::Page::Base class does not have views / elements defined!'
+          .to include 'Page class does not have views / elements defined!'
       end
     end
   end