calculateIsInsideBusinessHours.cls

global class calculateIsInsideBusinessHours {

    global class request
    {
        @InvocableVariable (label='Date' required = true)
        global DateTime givenDateTime;
        @InvocableVariable (label='Business Hours Id' required = true)
        global String businessHoursId;
    }

    global class response
    {
        @InvocableVariable (label='Is within Business Hours?')
        global Boolean dateInsideBusinessHours;
    }

    @InvocableMethod(label='Professor Flow | Calculate if date inside Business Hours' description='Returns true if the specified target date occurs within business hours. Holidays are included in the calculation.')
    global static List<response> DateInBusHours (List<request> inputParams)
    {
        //initialize response
        List<response> responseList = new List<response>();
        Boolean checkResult;
        if(inputParams != null && inputParams.size()> 0)
        {
            for(request pf : inputParams)
            {
                checkResult = BusinessHours.isWithin(pf.businessHoursId, pf.givenDateTime);
                response rs = new response();
                rs.dateInsideBusinessHours = checkResult;
                responseList.add(rs);
            }
        }
        return responseList;
    }
}

calculateIsInsideBusinessHoursTest.cls

@isTest
global class calculateIsInsideBusinessHoursTest 
{
    @isTest static void CheckDateInsideBusinessHours()
    {
        // Implement test code
        Profile sysadminprofile = [select Id, name from profile where Name = 'System administrator' limit 1];
        user adminUser = [select Id, Name from user where profileId= :sysadminprofile.Id  and isactive= True limit 1];
        businessHours bhoursId = [select Id from BusinessHours where name='Default' limit 1];
        System.runAs(adminUser)
        {
            List<calculateIsInsideBusinessHours.request> inputparams = new List<calculateIsInsideBusinessHours.request>();
            calculateIsInsideBusinessHours.request pf = new calculateIsInsideBusinessHours.request();
            pf.givendateTime = Datetime.now();
            pf.businessHoursId = bhoursId.Id;
            inputparams.add(pf);
            Test.startTest();
            List<calculateIsInsideBusinessHours.response> response = calculateIsInsideBusinessHours.DateInBusHours(inputParams);
            Test.stopTest();
            system.assertEquals(true, response[0].dateInsideBusinessHours);            
        }
        
    }
    
}