add validator for the 'reply_by_email_enabled' site setting

spec/components/validators/reply_by_email_enabled_validator_spec.rb

@@ -0,0 +1,31 @@
+require 'rails_helper'
+
+describe ReplyByEmailEnabledValidator do
+
+  describe '#valid_value?' do
+    subject(:validator) { described_class.new }
+
+    it "only validates when enabling the setting" do
+      expect(validator.valid_value?("f")).to eq(true)
+    end
+
+    it "returns false if reply_by_email_address is missing" do
+      SiteSetting.expects(:reply_by_email_address).returns("")
+      expect(validator.valid_value?("t")).to eq(false)
+    end
+
+    it "returns false if POP3 polling is disabled" do
+      SiteSetting.expects(:reply_by_email_address).returns("foo.%{reply_key}+42@bar.com")
+      SiteSetting.expects(:pop3_polling_enabled).returns(false)
+      expect(validator.valid_value?("t")).to eq(false)
+    end
+
+    it "returns true when POP3 polling is enabled and the reply_by_email_address is configured" do
+      SiteSetting.expects(:reply_by_email_address).returns("foo.%{reply_key}+42@bar.com")
+      SiteSetting.expects(:pop3_polling_enabled).returns(true)
+      expect(validator.valid_value?("t")).to eq(true)
+    end
+
+  end
+
+end