Some better errors when commands aren't found, and tests to ensure the errors show

lib/paperclip/geometry.rb

@@ -19,6 +19,8 @@ module Paperclip
                    Paperclip.run("identify", "-format %wx%h :file", :file => "#{file}[0]")
                  rescue Cocaine::ExitStatusError
                    ""
+                 rescue Cocaine::CommandNotFoundError => e
+                   raise Paperclip::CommandNotFoundError.new("Could not run the `identify` command. Please install ImageMagick.")
                  end
       parse(geometry) ||
         raise(NotIdentifiedByImageMagickError.new("#{file} is not recognized by the 'identify' command."))

lib/paperclip/thumbnail.rb

@@ -59,8 +59,10 @@ module Paperclip
         parameters = parameters.flatten.compact.join(" ").strip.squeeze(" ")
 
         success = Paperclip.run("convert", parameters, :source => "#{File.expand_path(src.path)}[0]", :dest => File.expand_path(dst.path))
-      rescue Cocaine::CommandLineError => e
+      rescue Cocaine::ExitStatusError => e
         raise PaperclipError, "There was an error processing the thumbnail for #{@basename}" if @whiny
+      rescue Cocaine::CommandNotFoundError => e
+        raise Paperclip::CommandNotFoundError.new("Could not run the `convert` command. Please install ImageMagick.")
       end
 
       dst

test/geometry_test.rb

@@ -120,6 +120,19 @@ class GeometryTest < Test::Unit::TestCase
       assert_raise(Paperclip::NotIdentifiedByImageMagickError){ @geo = Paperclip::Geometry.from_file(file) }
     end
 
+    should "let us know when a command isn't found versus a processing error" do
+      old_path = ENV['PATH']
+      begin
+        ENV['PATH'] = ''
+        assert_raises(Paperclip::CommandNotFoundError) do
+          file = File.join(File.dirname(__FILE__), "fixtures", "5k.png")
+          @geo = Paperclip::Geometry.from_file(file)
+        end
+      ensure
+        ENV['PATH'] = old_path
+      end
+    end
+
     [['vertical',   900,  1440, true,  false, false, 1440, 900, 0.625],
      ['horizontal', 1024, 768,  false, true,  false, 1024, 768, 1.3333],
      ['square',     100,  100,  false, false, true,  100,  100, 1]].each do |args|

test/thumbnail_test.rb

@@ -73,6 +73,18 @@ class ThumbnailTest < Test::Unit::TestCase
         @thumb = Paperclip::Thumbnail.new(@file, :geometry => "100x50#")
       end
 
+      should "let us know when a command isn't found versus a processing error" do
+        old_path = ENV['PATH']
+        begin
+          ENV['PATH'] = ''
+          assert_raises(Paperclip::CommandNotFoundError) do
+            @thumb.make
+          end
+        ensure
+          ENV['PATH'] = old_path
+        end
+      end
+
       should "report its correct current and target geometries" do
         assert_equal "100x50#", @thumb.target_geometry.to_s
         assert_equal "434x66", @thumb.current_geometry.to_s
@@ -182,6 +194,18 @@ class ThumbnailTest < Test::Unit::TestCase
             @thumb.make
           end
         end
+
+        should "let us know when a command isn't found versus a processing error" do
+          old_path = ENV['PATH']
+          begin
+            ENV['PATH'] = ''
+            assert_raises(Paperclip::CommandNotFoundError) do
+              @thumb.make
+            end
+          ensure
+            ENV['PATH'] = old_path
+          end
+        end
       end
     end