@Test
public void resolveContentTypeForFileNameTest() {

    final Function<String, String> target =
            RichMenuImageUploadCommand::resolveContentTypeForFileName;
    // Verify
    assertThat(target.apply("image.PNG")).isEqualTo("image/png");
    assertThat(target.apply("image.png")).isEqualTo("image/png");
    assertThat(target.apply("image.jpg")).isEqualTo("image/jpeg");
    assertThat(target.apply("image.jpeg")).isEqualTo("image/jpeg");
}