public void testNonEmpty_copy() throws IOException {
      fillContent("123456");
      RegularFile copy = file.copyWithoutContent(1, fileTimeSource.now());
      file.copyContentTo(copy);
      assertContentEquals("123456", copy);
    }
Actual test cases for testing RegularFiles.
jimfs/src/test/java/com/google/common/jimfs/RegularFileTest.java