This gist is part of the article http://codelectron.com/programming-lolin-d32-pro-esp32-board-using-arduino/

SDCard_test_d32.ino

#include "SD.h"
// https://github.com/espressif/arduino-esp32/blob/master/libraries/SPI/src/SPI.h
// https://wiki.wemos.cc/_media/products:d32:sch_d32_pro_v2.0.0.pdf
void setup() {
    Serial.begin(115200);
    SPI.begin(18, 19, 23, 4);

    if(!SD.begin(4)){
        Serial.println("Card Mount Failed");
        return;
    }
    uint64_t cardSize = SD.cardSize() / (1024 * 1024);
    Serial.printf("SD Card Size: %lluMB\n", cardSize);
}
void loop() {}