Add `File.exists?` to MRuby

This also enables file checking to the `Image` class for MRI and MRuby
(on the web, a “failed to load resource” already appears). Also, all
exceptions will now be printed in MRuby, yay!

1 files changed, 11 insertions, 0 deletions

diff --git a/test/image_spec.rb b/test/image_spec.rb
new file mode 100644
index 0000000..43950c9
--- /dev/null
+++ b/test/image_spec.rb
@@ -0,0 +1,11 @@
+require 'ruby2d'
+
+RSpec.describe Ruby2D::Image do
+  
+  describe '#new' do
+    it "raises exception if image file doesn't exist" do
+      expect { Image.new(0, 0, 'bad_image.png') }.to raise_error(Ruby2D::Error)
+    end
+  end
+  
+end