### Question:
Namespaces { public static String getInstanceGenerationPrefix(String instanceDir, long generationID) { Preconditions.checkArgument(generationID >= 0L, "Bad generation %s", generationID); return getInstancePrefix(instanceDir) + getPaddedGenerationID(generationID) + '/'; } private  Namespaces(); static Namespaces get(); String getPrefix(); static String getSysPrefix(String instanceDir); static String getKeystoreFilePrefix(String instanceDir); static Path toPath(String suffix); static String getInstancePrefix(String instanceDir); static String getInstanceGenerationPrefix(String instanceDir, long generationID); static String getTempPrefix(String instanceDir, long generationID); static String getIterationsPrefix(String instanceDir, long generationID); static String getGenerationDoneKey(String instanceDir, long generationID);  }### Answer:
@Test(expected = IllegalArgumentException.class) public void testNegativeGenerationID() throws Exception { Namespaces.getInstanceGenerationPrefix(ConfigUtils.getDefaultConfig().getString("model.instance-dir"), -1L); }