add build test using a build directory

lib/rscons/builders/program.rb

@@ -18,23 +18,25 @@ module Rscons
         if source.has_suffix?([@env['OBJSUFFIX'], @env['LIBSUFFIX']])
           source
         else
-          o_file = source.set_suffix(@env['OBJSUFFIX', :string])
+          o_file = @env.get_build_fname(source, @env['OBJSUFFIX', :string])
           builder = @env.builders.values.find { |b| b.produces?(o_file, source) }
           builder or raise "No builder found to convert input source #{source.inspect} to an object file."
-          builder.run(o_file, [source], cache)
+          builder.run(o_file, [source], cache) or break
         end
       end
-      vars = {
-        'TARGET' => target,
-        'SOURCES' => sources,
-        'LD' => @env['LD'] || @env['CC'], # TODO: figure out whether to use CC or CXX
-      }
-      command = @env.build_command(@env['LDCOM'], vars)
-      unless cache.up_to_date?(target, command, sources)
-        return false unless @env.execute("LD #{target}", command)
-        cache.register_build(target, command, sources)
+      if sources
+        vars = {
+          'TARGET' => target,
+          'SOURCES' => sources,
+          'LD' => @env['LD'] || @env['CC'], # TODO: figure out whether to use CC or CXX
+        }
+        command = @env.build_command(@env['LDCOM'], vars)
+        unless cache.up_to_date?(target, command, sources)
+          return false unless @env.execute("LD #{target}", command)
+          cache.register_build(target, command, sources)
+        end
+        target
       end
-      target
     end
   end
 end

lib/rscons/environment.rb

@@ -99,7 +99,7 @@ module Rscons
 
     def execute(short_desc, command)
       if @varset[:echo] == :command
-        puts command.map { |c| c =~ /\s/ ?  "'#{c}'" : c }.join(' ')
+        puts command.map { |c| c =~ /\s/ ? "'#{c}'" : c }.join(' ')
       elsif @varset[:echo] == :short
         puts short_desc
       end