SystemInfo { public static String os() { StringBuilder sb = new StringBuilder(); sb .append(system.getProperty("os.name")) .append(" ") .append(system.getProperty("os.version")) .append(" ") .append(system.getProperty("os.arch")); return sb.toString(); } private  SystemInfo(); static void setSystem(System2 system); static String getVersion(); static String java(); static String os();  }
@Test public void test_os() { mockOs(); assertThat(SystemInfo.os()).isEqualTo("linux 2.5 x64"); }