Add "test" rscons task

Rsconscript

@@ -2,10 +2,19 @@ configure do
   check_d_compiler
 end
 
-env do |env|
+fart_env = env "fart" do |env|
   env["DFLAGS"] += %w[-Werror -O2]
   env["D_IMPORT_PATH"] += %w[src]
 
-  sources = glob("src/**/*.d")
-  env.Program("fart", sources)
+  env["sources"] = glob("src/**/*.d")
+  env.Program("fart", "${sources}")
+end
+
+task "test" do
+  test_env = fart_env.clone "test" do |env|
+    env["DFLAGS"] += %w[-funittest]
+    env.Program("^/farttest", "${sources}")
+  end
+  test_env.process
+  sh test_env.expand("^/farttest")
 end