public static Schema convert(final org.apache.iceberg.Schema schema) {
    ImmutableList.Builder<Field> fields = ImmutableList.builder();

    for (NestedField f : schema.columns()) {
      fields.add(convert(f));
    }

    return new Schema(fields.build());
  }
@Test
  public void convertComplex() {
    Schema iceberg =
        new Schema(
            Types.NestedField.optional(
                0, "m", MapType.ofOptional(1, 2, StringType.get(), LongType.get())),
            Types.NestedField.required(
                3,
                "m2",
                MapType.ofOptional(
                    4, 5, StringType.get(), ListType.ofOptional(6, TimestampType.withoutZone()))));
    org.apache.arrow.vector.types.pojo.Schema arrow = ArrowSchemaUtil.convert(iceberg);
    assertThat(arrow.getFields()).hasSameSizeAs(iceberg.columns());
  }