Using unless instead of if not

testing/lib/refinery/tasks/testing.rake

@@ -1,4 +1,4 @@
-namespace :refinery do 
+namespace :refinery do
   namespace :testing do
     desc "Generates a dummy app for testing"
     task :dummy_app => [:setup_dummy_app, :migrate_dummy_app]
@@ -23,10 +23,10 @@ namespace :refinery do
     end
 
     task :migrate_dummy_app do
-      if !defined?(ENGINE_PATH) || !ENGINE_PATH
+      unless defined?(ENGINE_PATH) && ENGINE_PATH
         abort("ERROR: ENGINE_PATH must be defined and contain a path pointing to your engine's root.")
       end
-      
+
       engines = [
         'refinery_core',
         'refinery_settings',
@@ -41,10 +41,10 @@ namespace :refinery do
 
     desc "Remove the dummy app used for testing"
     task :clean_dummy_app do
-      if !defined?(ENGINE_PATH) || !ENGINE_PATH
+      unless defined?(ENGINE_PATH) && ENGINE_PATH
         abort("ERROR: ENGINE_PATH must be defined and contain a path pointing to your engine's root.")
       end
-      
+
       system "rm -Rdf #{File.join(ENGINE_PATH, 'spec/dummy')}"
     end