Here is a nice graph about the data verification technology in SD Card Test Pro Android application:
Data verification technology (Verify written data): This is a professional feature in SD Card Test Pro app. When you enable this feature, the application will generate and write random data to the disk. During the write, it calculates the hash of the random data and stores it. When you run a read test, the app will read the random data from the disk and it calculates the hash of the read data.
When read test is finished, SD Card Test Pro will compare the hashes of the written and the read data. If they are the same, the card is not damaged and what’s more important, it could store as many data on the disk safely as you set in the settings in file size. If the hashes are different, then either the SD card is damaged or fake.
How to set it in the app (YouTube video):