interface BrandController {
    fun findDTOs(pageable: Pageable): ResponseEntity<Page<SomeDTO>>
}

var response: ResponseEntity<*>

@Test
fun `test`() {
    `given TestRestTemplate`()
    `when findDTOs`()
    `then check body`()
}

protected fun `given not authorization`() {
    restTemplate = TestRestTemplate()
}

private fun `when findDTOs`() {
    // RestResponsePage<T> extends PageImpl<T>
    response = restTemplate.getForEntity<RestResponsePage<SomeDTO>>(createUrlWithParams(url, requestPage))
}

private fun `then check body`() {
    val body: Page<SomeDTO> = response.body as Page<SomeDTO> // body: "Page 2 of 2 containing java.util.LinkedHashMap instances"

    assertEquals(requestPage.size, body.size) // success

    val content: List<SomeDTO> = body.content as List<SomeDTO> // content: size = 10 body: "Page 2 of 2 containing java.util.LinkedHashMap instances"

    brands.forEachIndexed { index, someDTO: SomeDTO-> //Error
        assertEquals(list[index].name, someDTO.name)
        assertEquals(list[index].id, someDTO.id)
    }
}

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com....SomeDTO