Add a test for container repository name regexp

lib/gitlab/regex.rb

@@ -28,6 +28,10 @@ module Gitlab
       @container_repository_regex ||= %r{\A[a-z0-9]+(?:[-._/][a-z0-9]+)*\Z}
     end
 
+    ##
+    # We do not use regexp anchors here because these are not allowed when
+    # used as a routing constraint.
+    #
     def container_registry_tag_regex
       @container_registry_tag_regex ||= /[\w][\w.-]{0,127}/
     end

spec/lib/gitlab/regex_spec.rb

@@ -38,4 +38,15 @@ describe Gitlab::Regex, lib: true do
     it { is_expected.not_to match('9foo') }
     it { is_expected.not_to match('foo-') }
   end
+
+  describe '.container_repository_name_regex' do
+    subject { described_class.container_repository_name_regex }
+
+    it { is_expected.to match('image') }
+    it { is_expected.to match('my/image') }
+    it { is_expected.to match('my/awesome/image-1') }
+    it { is_expected.to match('my/awesome/image.test') }
+    it { is_expected.not_to match('.my/image') }
+    it { is_expected.not_to match('my/image.') }
+  end
 end