Add validation specs to CustomFilter model (#28600)

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