refining and getting tests for placeholder

samples/images/_placeholders.rb

@@ -16,13 +16,28 @@ Squib::Deck.new(width: 100, height: 100, cards: 3) do
 end
 
 # Placeholders can be per-image too.
-# What if a placeholder is specified but doesn't exist?
-# It'll always warn.
-Squib::Deck.new(width: 100, height: 100, cards: 3) do
+# What if a placeholder is specified but doesn't exist? It'll always warn.
+Squib.configure img_missing: :warn # default
+Squib::Deck.new(width: 100, height: 100, cards: 4) do
   background color: :white
 
-  files =        %w(angler-fish.png does-not-exist.png does-not-exist.png)
-  placeholders = %w(grit.png        does-not-exist.png grit.png)
+  files =        %w(angler-fish.png does-not-exist.png does-not-exist.png does-not-exist.png)
+  placeholders = %w(grit.png        does-not-exist.png grit.png                             )
   png file: files, placeholder: placeholders
   save_sheet columns: 1, prefix: 'multi_placeholder_sheet_'
+end
+
+# Do errors work?
+# If you REALLY want the old, pre-Squib v0.18 functionality
+# ...you can still have it
+# This is really more of a regression test than example.
+Squib.configure img_missing: :error
+Squib::Deck.new(width: 100, height: 100, cards: 1) do
+  begin
+    png file: 'does-not-exist.png' # no placeholder... should error!
+    raise Exception.new 'Runtime Error should have been thrown!'
+  rescue RuntimeError => e
+    # a runtime error should have happened here. So nothing happens. Good.
+    Squib.logger.error 'Yay! An error we expected was thrown.'
+  end
 end