Coverage improvement round-out following up previous work (#23987)

spec/lib/importer/base_importer_spec.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe Importer::BaseImporter do
+  describe 'import!' do
+    let(:pool) { Concurrent::FixedThreadPool.new(5) }
+    let(:importer) { described_class.new(batch_size: 123, executor: pool) }
+
+    it 'raises an error' do
+      expect { importer.import! }.to raise_error(NotImplementedError)
+    end
+  end
+end