Implement `has_file' condition keyword

lib/producer/core.rb

@@ -6,6 +6,7 @@ require 'producer/core/actions/shell_command'
 # condition tests (need to be defined before the condition DSL)
 require 'producer/core/test'
 require 'producer/core/tests/has_env'
+require 'producer/core/tests/has_file'
 
 require 'producer/core/cli'
 require 'producer/core/condition'

lib/producer/core/condition/dsl.rb

@@ -16,7 +16,8 @@ module Producer
           end
         end
 
-        define_test :has_env, Tests::HasEnv
+        define_test :has_env,   Tests::HasEnv
+        define_test :has_file,  Tests::HasFile
 
         attr_accessor :tests
 

lib/producer/core/tests/has_file.rb

@@ -0,0 +1,11 @@
+module Producer
+  module Core
+    module Tests
+      class HasFile < Test
+        def success?
+          env.remote.fs.has_file? arguments.first
+        end
+      end
+    end
+  end
+end