public void testNonEmpty_write_partial_fromBeforeEnd_multipleBuffers() throws IOException {
      fillContent("22222222");
      assertEquals(6, file.write(6, buffers("111", "333")));
      assertContentEquals("222222111333", file);
    }
Actual test cases for testing RegularFiles.
jimfs/src/test/java/com/google/common/jimfs/RegularFileTest.java