DEV: Validate that passed in groups exist in AtLeastOneGroupValidator (#24890)

This validator is used for site settings where one or more groups are to be input.

At the moment this validator just checks that the value isn't blank. This PR adds a validation for the existence of the groups passed in.

lib/validators/at_least_one_group_validator.rb

@@ -3,13 +3,25 @@
 class AtLeastOneGroupValidator
   def initialize(opts = {})
     @opts = opts
+    @invalid_groups = []
   end
 
   def valid_value?(val)
-    val.present? && val != ""
+    @invalid_groups = []
+
+    return false if val.blank?
+
+    group_ids = val.to_s.split("|").map(&:to_i)
+
+    @invalid_groups = group_ids - Group.where(id: group_ids).pluck(:id)
+    @invalid_groups.empty?
   end
 
   def error_message
-    I18n.t("site_settings.errors.at_least_one_group_required")
+    if @invalid_groups.empty?
+      I18n.t("site_settings.errors.at_least_one_group_required")
+    else
+      I18n.t("site_settings.errors.invalid_group")
+    end
   end
 end

spec/lib/validators/at_least_one_group_validator_spec.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+RSpec.describe AtLeastOneGroupValidator do
+  subject(:validator) { described_class.new }
+
+  describe "#valid_value?" do
+    context "when using a blank value" do
+      it { expect(validator.valid_value?(nil)).to eq(false) }
+    end
+
+    context "when one of the groups doesn't exist" do
+      it { expect(validator.valid_value?("10|1337")).to eq(false) }
+    end
+
+    context "when all the groups exist" do
+      it { expect(validator.valid_value?("10|11")).to eq(true) }
+    end
+  end
+
+  describe "#error_message" do
+    context "when using a blank value" do
+      before { validator.valid_value?(nil) }
+
+      it do
+        expect(validator.error_message).to eq(
+          "You must specify at least one group for this setting.",
+        )
+      end
+    end
+
+    context "when one of the groups doesn't exist" do
+      before { validator.valid_value?("10|1337") }
+
+      it { expect(validator.error_message).to eq("There's no group with that name.") }
+    end
+  end
+end