Fix preflight exception when file row has no files (#271)

**ISSUE**
When importing a CSV without a "files" column, preflight was throwing
an exception when trying to upack nil files.

**SOLUTION**
We don't want to make "files" a required column, because it's totally
valid to import a CSV with only Collections.  This change detects when
`files` in a a row with object type "File" is nil or empty and creates
a placeholder error `PFFile` object to store the relevant row-level warnings.

**OTHER CHANGES**
This commit also splits the Preflight and PreFlightObj tests into two
files since the preflight spec file was getting pretty long.

see spec/lib/tenejo/pre_flight_obj_spec.rb:26-40 for the new tests.

app/lib/tenejo/pf_object.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 module Tenejo
-  LICENSES = YAML.safe_load(File.open(Rails.root.join("config/authorities/licenses.yml")))
-
   class LicenseValidator < ActiveModel::Validator
     def validate(record)
       licenses = Array.wrap(record.license).select(&:present?)
@@ -203,6 +201,7 @@ def self.exist?(rec, val)
     end
 
     def self.unpack(row, lineno, import_root)
+      return [invalid_file(row, lineno)] if row[:files].blank?
       cp = row.dup
       index = 1
       packed = row[:files].include?("|~|")
@@ -217,6 +216,10 @@ def self.unpack(row, lineno, import_root)
       files
     end
 
+    def self.invalid_file(row, lineno)
+      PFFile.new(row, lineno, '')
+    end
+
     def initialize(row = {}, lineno = 0, import_root = true, strict_paths = true)
       file_name = row.to_h.delete(:files)
       row[:file] = relative_path(file_name, import_root, strict_paths)

spec/fixtures/csv/fancy.csv

@@ -8,3 +8,4 @@ MPC003,W,TESTINGCOLLECTION,"TEST Postcards - Minneapolis UNPACKED FILES - Lake H
 ,F,MPC003,,,,,,MN-02 4.png,Image,,,,,,,,,,,
 MPC008,W,MPC003,"TEST Postcards - Minneapolis UNPACKED FILES - Lake Harriet, Minneapolis, Minn",Bloom Bros Co.,postcard|~|Minneapolis|~|Lake Harriet,https://rightsstatements.org/vocab/NoC-OKLR/1.0/,open,,Image,Postcard depicting Lake Harriet,,https://creativecommons.org/publicdomain/mark/1.0/,,1900-1945,Postcards,English,,,,
 MPC009,WOrK,NONA,"TEST Postcards - Minneapolis UNPACKED FILES - Lake Harriet, Minneapolis, Minn",Bloom Bros Co.,postcard|~|Minneapolis|~|Lake Harriet,https://rightsstatements.org/vocab/NoC-OKLR/1.0/,open,,Image,Postcard depicting Lake Harriet,,https://creativecommons.org/publicdomain/mark/1.0/,,1900-1945,Postcards,English,,,,
+,File,,"File missing identifier, parent, and file",,,,open,,,,,,,,,,,,,

spec/lib/tenejo/csv_importer_spec.rb

@@ -36,19 +36,20 @@
       csv_import = described_class.new(import_job)
       expect(import_job.status).to eq 'submitted'
       expect(csv_import.preflight_errors).to eq []
-      expect(csv_import.invalid_rows).to eq []
+      expect(csv_import.invalid_rows).to include a_hash_including('lineno' => 11)
       expect(csv_import.preflight_warnings)
         .to contain_exactly(
               "The column \'Comment\' is unknown and will be ignored",
-              "Row 3: Could not find parent \'NONEXISTENT\'; collection \'NONACOLLECTION\' will be created without a parent if you continue.",
-              "Row 6: Could not find parent work \'WHUT?\' for file \'MN-02 2.png\' - the file will be ignored",
-              "Row 10: Could not find parent \'NONA\'; work \'MPC009\' will be created without a parent if you continue.",
               "Row 2: Resource Type \'Photos\' is not recognized and will be omitted.",
+              "Row 3: Could not find parent \'NONEXISTENT\'; collection \'NONACOLLECTION\' will be created without a parent if you continue.",
               "Row 3: Resource Type \'Posters\' is not recognized and will be omitted.",
               "Row 5: Visibility is blank - and will be treated as private",
               "Row 5: Visibility is blank - and will be treated as private",
               "Row 6: Visibility is blank - and will be treated as private",
-              "Row 8: Visibility is blank - and will be treated as private"
+              "Row 8: Visibility is blank - and will be treated as private",
+              "Row 6: Could not find parent work \'WHUT?\' for file \'MN-02 2.png\' - the file will be ignored",
+              "Row 10: Could not find parent \'NONA\'; work \'MPC009\' will be created without a parent if you continue.",
+              "Row 11: Parent can't be blank, File can't be blank, Identifier can't be blank"
             )
     end
   end

spec/lib/tenejo/graph_spec.rb

@@ -1,32 +1,32 @@
 # frozen_string_literal: true
 require 'rails_helper'
-RSpec.describe Tenejo::Graph do
+RSpec.describe Tenejo::Graph, :aggregate_failures do
   context "when empty" do
-    let(:g) { described_class.new }
+    let(:graph) { described_class.new }
     it "can serialize to json" do
-      expect(g.to_json).not_to be_nil
-      expect(JSON.parse(g.to_json)).not_to be_nil
-      expect(JSON.parse(g.to_json).class).to eq Hash
+      expect(graph.to_json).not_to be_nil
+      expect(JSON.parse(graph.to_json)).not_to be_nil
+      expect(JSON.parse(graph.to_json).class).to eq Hash
     end
   end
 
   context "having loaded a file" do
-    let(:g) {
+    let(:graph) {
       allow(File).to receive(:exist?).and_call_original
       allow(File).to receive(:exist?).with(/tiff/).and_return(true)
       allow(File).to receive(:exist?).with(/png/).and_return(true)
       Tenejo::Preflight.process_csv(File.open("./spec/fixtures/csv/nesting_test.csv"))
     }
-    let(:flat) { g.flatten }
+    let(:flat) { graph.flatten }
 
-    let(:j) { Job.create!(user: FactoryBot.create(:user), graph: g) }
+    let(:j) { Job.create!(user: FactoryBot.create(:user), graph: graph) }
 
     it "finds all the files" do
       expect(j.graph.files.count).to eq 17
     end
 
     it "empties out the detached files list after attaching them" do
-      expect(g.detached_files).to be_empty
+      expect(graph.detached_files).to be_empty
     end
 
     it "is able to reify after reload" do