when u are writing a test class u need some test data , which will not reflect on actual data

Note any record created in test class in not updated in real database

you can create test data in @testSetup meathod (best practice)

then create testMeathod and call the class and check for assert

in the below case i called a custom controler to check if records are creted properly

/**
* This class contains unit tests for validating the behavior of Apex classes
* and triggers.
*
* Unit tests are class methods that verify whether a particular piece
* of code is working properly. Unit test methods take no arguments,
* commit no data to the database, and are flagged with the testMethod
* keyword in the method definition.
*
* All test methods in an organization are executed whenever Apex code is deployed
* to a production organization to confirm correctness, ensure code
* coverage, and prevent regressions. All Apex classes are
* required to have at least 75% code coverage in order to be deployed
* to a production organization. In addition, all triggers must have some code coverage.
*
* The @isTest class annotation indicates this class only contains test
* methods. Classes defined with the @isTest annotation do not count against
* the organization size limit for all Apex scripts.
*
* See the Apex Language Reference for more information about Testing and Code Coverage.
*/

@isTest(seeAllData=false) 
public class TestMemberControler {
     
    @testSetup
    /**
*     Description     :   Test data for bank management system
*
*     Created By      :   Ishan Arora
*
*     @return         :      void
**/
    Static void testData () {
        
         //Creating a list of house
        List<House__c> listHouseId = new List<House__c>();
       
        //Creating a list of persons
        List<Person__c> persons = new List<Person__c>();
       
        //Add the list with the house details
        listHouseId.add(new House__c(Name='Jalsa', Address__c='Mumbai'));
       
        //update the person list with all the person details
        persons.add(new Person__c(Name='Ayush',Gender__c='Male', Birthday__c= System.today() ));
        persons.add(new Person__c(Name='Sharad',Gender__c='Male', Birthday__c= System.today()));
       
        //insert the record of house
        insert listHouseId;
       
        //insert the record of persons
        insert persons;
               
    }
    
    /**
	*     Description     :   This method is used to test save meathod in Add Member class
	*
	*     Created By      :   Ishan Arora
	*
	*     @return         :      void
	*
	**/
    static testMethod void testAddMember() {
        
        //Making Instance of Controller
        MemberControler obj = new MemberControler();
        
        //Getting id of house
        List<House__c> listHouseId = [Select Id from House__c];
        
        //Getting id of Person
        List<Person__c> persons = [Select id from Person__C];
        
        //Adding data of member to Member variable
        obj.member = new Member__c(Name='Ayush',House__c=listHouseId[0].Id,Person__c = persons[0].Id);
        
        //Calling controller meathod
        obj.save();
        
        //Query to get stored Record
        List <Member__c> insertedMember = [Select Name, House__c, Person__c from Member__c limit 1];
        
        //Assert to check expected against Actual value
        System.assertEquals('Ayush', insertedMember[0].Name);
        System.assertEquals(listHouseId[0].Id, insertedMember[0].House__c);
        System.assertEquals(persons[0].Id, insertedMember[0].Person__c);
        
        
    }
    
}