test: that extra invalid field labels don't cause issues

spec/services/bulk_upload/lettings/year2023/csv_parser_spec.rb

@@ -79,6 +79,33 @@ RSpec.describe BulkUpload::Lettings::Year2023::CsvParser do
     end
   end
 
+  context "when parsing csv with extra invalid headers" do
+    let(:seed) { rand }
+    let(:log_to_csv) { BulkUpload::LogToCsv.new(log:) }
+    let(:field_numbers) { log_to_csv.default_2023_field_numbers + ["invalid_field_number"] }
+    let(:field_values) { log_to_csv.to_2023_row + ["value_for_invalid_field_number"] }
+
+    before do
+      file.write("Question\n")
+      file.write("Additional info\n")
+      file.write("Values\n")
+      file.write("Can be empty?\n")
+      file.write("Type of letting the question applies to\n")
+      file.write("Duplicate check field?\n")
+      file.write(log_to_csv.custom_2023_field_numbers_row(seed:, field_numbers:))
+      file.write(log_to_csv.to_custom_2023_csv_row(seed:, field_values:))
+      file.rewind
+    end
+
+    it "parses csv correctly" do
+      expect(service.row_parsers[0].field_13).to eql(log.tenancycode)
+    end
+
+    it "counts the number of valid field numbers correctly" do
+      expect(service.valid_field_numbers_count).to eql(134)
+    end
+  end
+
   context "when parsing csv without headers" do
     before do
       file.write(BulkUpload::LogToCsv.new(log:, col_offset: 0).to_2023_csv_row)