Add validation specs to `CustomFilter` model (#28600)

app/models/custom_filter.rb

@@ -143,6 +143,10 @@ class CustomFilter < ApplicationRecord
   end
 
   def context_must_be_valid
-    errors.add(:context, I18n.t('filters.errors.invalid_context')) if context.empty? || context.any? { |c| !VALID_CONTEXTS.include?(c) }
+    errors.add(:context, I18n.t('filters.errors.invalid_context')) if invalid_context_value?
+  end
+
+  def invalid_context_value?
+    context.blank? || context.difference(VALID_CONTEXTS).any?
   end
 end

spec/models/custom_filter_spec.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe CustomFilter do
+  describe 'Validations' do
+    it 'requires presence of title' do
+      record = described_class.new(title: '')
+      record.valid?
+
+      expect(record).to model_have_error_on_field(:title)
+    end
+
+    it 'requires presence of context' do
+      record = described_class.new(context: nil)
+      record.valid?
+
+      expect(record).to model_have_error_on_field(:context)
+    end
+
+    it 'requires non-empty of context' do
+      record = described_class.new(context: [])
+      record.valid?
+
+      expect(record).to model_have_error_on_field(:context)
+    end
+
+    it 'requires valid context value' do
+      record = described_class.new(context: ['invalid'])
+      record.valid?
+
+      expect(record).to model_have_error_on_field(:context)
+    end
+  end
+end