Example of a Post Install Script

Salesforce Example of a Post Install Script
The following sample post install script performs these actions on package install/upgrade.
If the previous version is null, that is, the package is being installed for the first time, the script:
Creates a new Account called “Newco” and verifies that it was created.
Creates a new instance of the custom object Survey, called “Client Satisfaction Survey”.
Sends an email message to the subscriber confirming installation of the package.
If the previous version is 1.0, the script creates a new instance of Survey called “Upgrading from Version 1.0”.
If the package is an upgrade, the script creates a new instance of Survey called “Sample Survey during Upgrade”.
If the upgrade is being pushed, the script creates a new instance of Survey called “Sample Survey during Push”.
global class PostInstallClass implements InstallHandler {
  global void onInstall(InstallContext context) {
    if(context.previousVersion() == null) {
      Account a = new Account(name='Newco');
      insert(a);
      
      Survey__c obj = new Survey__c(name='Client Satisfaction Survey');
      insert obj;
               
      User u = [Select Id, Email from User where Id =:context.installerID()];   
      String toAddress= u.Email;
      String[] toAddresses = new String[]{toAddress};
      Messaging.SingleEmailMessage mail = 
        new Messaging.SingleEmailMessage();
      mail.setToAddresses(toAddresses);
      mail.setReplyTo('support@package.dev');
      mail.setSenderDisplayName('My Package Support');
      mail.setSubject('Package install successful');
      mail.setPlainTextBody('Thanks for installing the package.');
      Messaging.sendEmail(new Messaging.Email[] { mail });
      }
    else
      if(context.previousVersion().compareTo(new Version(1,0)) == 0) {
      Survey__c obj = new Survey__c(name='Upgrading from Version 1.0');
      insert(obj);
      }
    if(context.isUpgrade()) {
      Survey__c obj = new Survey__c(name='Sample Survey during Upgrade');
      insert obj;
      }
    if(context.isPush()) {
      Survey__c obj = new Survey__c(name='Sample Survey during Push');
      insert obj;
      }
    }
  }

You can test a post install script using the new testInstall method of the Test class. This method takes the following arguments.
A class that implements the InstallHandler interface.
A Version object that specifies the version number of the existing package.
An optional Boolean value that is true if the installation is a push. The default is false.
This sample shows how to test a post install script implemented in the PostInstallClass Apex class.

@isTest
static void testInstallScript() {
  PostInstallClass postinstall = new PostInstallClass();
    Test.testInstall(postinstall, null);
    Test.testInstall(postinstall, new Version(1,0), true);
    List<account> a = [Select id, name from Account where name ='Newco'];
    System.assertEquals(a.size(), 1, 'Account not found');
  }