Fix #5140: Unexpected error: PublicSuffix::DomainInvalid for searching some newgrounds urls in /artists

When the artist name couldn't found for a Newgrounds URL, for example
for `https://www.newgrounds.com/dump/item`, then the `profile_url`
method erroneously returned `https://.newgrounds.com`. This led to an
error later on when the artist finder tried to parse the invalid URL.

Also fix `strategy_should_work` to test that the profile URL is a valid
URL, and not to try to download the file when image_urls is empty.

app/logical/source/extractor/newgrounds.rb

@@ -60,7 +60,7 @@ module Source
       def profile_url
         # user names are not mutable, artist names are.
         # However we need the latest name for normalization
-        "https://#{artist_name}.newgrounds.com"
+        "https://#{artist_name}.newgrounds.com" if artist_name.present?
       end
 
       def artist_commentary_title

test/test_helpers/source_test_helper.rb

@@ -20,7 +20,7 @@ module SourceTestHelper
       assert_not(strategy.image_urls.include?(nil))
     end
 
-    should_download_successfully(strategy, download_size) unless deleted
+    should_download_successfully(strategy, download_size) unless deleted || strategy.image_urls.empty?
 
     # {profile_url: nil}[:profile_url].present? -> false
     # Doing it this way instead we can check profile_url even if it's passed as a nil.
@@ -49,6 +49,7 @@ module SourceTestHelper
   def should_handle_artists_correctly(strategy, profile_url)
     if profile_url.present?
       should "correctly match a strategy to an artist with the same profile url" do
+        assert_not_nil(Danbooru::URL.parse(strategy.profile_url))
         assert_equal(profile_url, strategy.profile_url)
         artist = FactoryBot.create(:artist, name: strategy.artist_name, url_string: profile_url)
         assert_equal([artist], strategy.artists)

test/unit/artist_test.rb

@@ -402,6 +402,16 @@ class ArtistTest < ActiveSupport::TestCase
       end
     end
 
+    context "when finding Newgrounds artists" do
+      should "find the correct artist" do
+        create(:artist, name: "lasterk", url_string: "http://lasterk.newgrounds.com")
+        create(:artist, name: "merunyaa",  url_string: "https://merunyaa.newgrounds.com")
+
+        assert_artist_found("lasterk", "https://www.newgrounds.com/art/view/lasterk/booette")
+        assert_artist_not_found("https://www.newgrounds.com/dump/item/a1f417d20f5eaef31e26ac3c4956b3d4")
+      end
+    end
+
     context "the #normalize_other_names method" do
       subject { build(:artist) }
 

test/unit/sources/newgrounds_test.rb

@@ -98,6 +98,15 @@ module Sources
       end
     end
 
+    context "A www.newgrounds.com/dump/item URL" do
+      strategy_should_work(
+        "https://www.newgrounds.com/dump/item/a1f417d20f5eaef31e26ac3c4956b3d4",
+        image_urls: [],
+        artist_name: nil,
+        profile_url: nil,
+      )
+    end
+
     context "A post with links to other illustrations in the commentary" do
       should "not include the links in the commentary" do
         @source = Source::Extractor.find("https://www.newgrounds.com/art/view/boxofwant/annie-hughes-1")