CreatedDateでのソートはアテにならない

CreatedDateTest.cls

@isTest
public class CreatedDateTest {

    public static testMethod void run() {
        Account a = new Account();
        a.Name = 'Account # 1';
        insert a;
        System.debug(LoggingLevel.INFO, 'A\'s id: ' + a.id);

        Account b = new Account();
        b.Name = 'Account # 2';
        insert b;
        System.debug(LoggingLevel.INFO, 'B\'s id: ' + b.id);
        
        // assertion
        Account result = [SELECT Id FROM Account ORDER BY CreatedDate DESC LIMIT 1];
	System.debug(LoggingLevel.INFO, 'Result\'s id: ' + result.id);
        System.assertEquals(b.id, result.id);  // FAIL
    }
}