TestVisible annotation allow test methods to access private or protected members of another class outside the test class. These members include methods, member variables, and inner classes. This annotation enables a more permissive access level for running tests only. This annotation doesn’t change the visibility of members if accessed by non-test classes.

With this annotation, you don’t have to change the access modifiers of your methods and member variables to public if you want to access them in a test method. For example, if a private member variable isn’t supposed to be exposed to external classes but it should be accessible by a test method, you can add the TestVisible annotation to the variable definition.

This example shows how to annotate a private class member variable and private method with TestVisible and how to access it in test class.

Sample Class:

public class TestVisibleExample {
    //Private member variable
    @TestVisible private static Integer recordNumber = 1;

    //Private method
    @TestVisible private static void updateRecord(String name) {
        // Do something
    }
}    

Test Class:

@isTest
private class TestVisibleExampleTest {
    @isTest static void test1() {
        // Access private variable annotated with TestVisible
        Integer i = TestVisibleExample.recordNumber;
        System.assertEquals(1, i);

        // Access private method annotated with TestVisible
        TestVisibleExample.updateRecord('RecordName');
        // Perform some verification
    }
}

Generally, all Apex code runs in system mode, where the permissions and record sharing of the current user are not taken into account. The system method runAs enables you to write test methods that change the user context to an existing user or a new user so that the user’s record sharing is enforced. The runAs method doesn’t enforce user permissions or field-level permissions, only record sharing.

Note: We can use runAs only in test methods. The original system context is started again after all runAs test methods complete. The runAs method ignores user license limits. We can create new users with runAs even if your organization has no additional user licenses.

The following items use the permissions granted by the user specified with runAs running as a specific user:

• dynamic Apex
• methods using with sharing or without sharing
• shared records

Example:

In the following example, a new test user is created, then code is run as that user, with that user’s record sharing access:

@isTest
private class TestRunAs {
   public static testMethod void testRunAs() {
      // Setup test data
      // This code runs as the system user
      Profile p = [SELECT Id FROM Profile WHERE Name='Standard Test User']; 
      User u = new User(Alias = 'standt', Email='standardtestuser@force.com', 
      EmailEncodingKey='UTF-8', LastName='TestUser', LanguageLocaleKey='en_US', 
      LocaleSidKey='en_US', ProfileId = p.Id, 
      TimeZoneSidKey='America/Los_Angeles', UserName='standardtestuser@force.com');

      System.runAs(u) {
         // The following code runs as user 'u' 
         System.debug('Current User: ' + UserInfo.getUserName());
         System.debug('Current Profile: ' + UserInfo.getProfileId()); 
      }
   }
}