code: public @NotNull FileAssert hasSize(long expected) {
      isNotNull();
      long size = actual.length();
      if (size == expected) {
        return this;
      }
      failIfCustomMessageIsSet();
      throw failure(format("size of file:<%s> expected:<%s> but was:<%s>", actual, expected, size));
    }
docs: Verifies that the size of the actual {@code File} is equal to the given one.
  
  @param expected the expected size of the actual {@code File}.
  @return this assertion object.
  @throws AssertionError if the the actual {@code File} is {@code null}.
  @throws AssertionError if the size of the actual {@code File} is not equal to the given one.