Simulating date/time in apex for accurate, time-based testing

ProductionCode.cls

public with sharing class ProductionCode.cls {
    
    ...
    
    private static void scheduleBatchExecution(){
        
        ...
        
        //Use in place of DateTime.now()
        DateTime nowDT = Utilities.getCurrentDateTime();
      
        ...
      
    }
    
    ...
    
}

TestCode.cls

@IsTest private class TestCode {

    ...
    
    private static testMethod void simulateCurrentDateTime(){
    
        ...
        
        //Set the current date time to test a maintnenance window or other time-specific scheduling logic
        Utilities.testDateTime = DateTime.newInstance(Date.Today(), Time.newInstance(9, 0, 0, 0));
        
        ...
    
    }
    
    ...
    
}

Utilities.cls

public with sharing class Utilities {

    ...
 
    public static DateTime testDateTime;

    ...

    //Used to enable testing of logic that is dependent on the current dateTime;
    //This will be called in place of DateTime.now() by functional code
    public static DateTime getCurrentDateTime(){
        if(Test.isRunningTest() && testDateTime != NULL){
            return testDateTime;
        } else {
            return DateTime.now();
        }
    }

    //Used to enable testing of logic that is dependent on the current dateTime;
    //This will be called in place of Date.today() by functional code
    public static Date getCurrentDate(){
        if(Test.isRunningTest() && testDateTime != NULL){
            return testDateTime.date();
        } else {
            return Date.today();
        }
    }

    ...

}