@CanIgnoreReturnValue
  public PathSubject containsBytes(byte[] bytes) throws IOException {
    isRegularFile();
    hasSize(bytes.length);

    byte[] actual = Files.readAllBytes(this.actual);
    if (!Arrays.equals(bytes, actual)) {
      System.out.println(BaseEncoding.base16().encode(actual));
      System.out.println(BaseEncoding.base16().encode(bytes));
      failWithActual("expected to contain bytes", BaseEncoding.base16().encode(bytes));
    }
    return this;
  }
Asserts that the file is a regular file containing exactly the given bytes.
jimfs/src/test/java/com/google/common/jimfs/PathSubject.java