trigger AssignPermissionSet on User (after insert,after Update) {
PermissionSet pereset = [SELECT Id FROM PermissionSet WHERE Label ='SBU Impact Visible'];
Set<ID> addIds = new Set<Id>(),
        removeIds = new Set<Id>(),
        roleIds = new Map<Id, UserRole>([
    SELECT  Id FROM UserRole
    WHERE   Name LIKE '%E&C%' OR Name LIKE '%Commerical Ops%' OR Name LIKE
 '%Energy & Chemicals%' OR Name LIKE '%All Fluor%'
    OR Name LIKE '%System Administrator%'
]).keySet();
for(User record: Trigger.new) {
    (record.IsActive && roleIds.contains(record.UserRoleId)? addIds: removeIds).add(record.Id);
}
  PermissionSetAssignment[] permissionSetList = new PermissionSetAssignment[0];
addIds.removeAll(new Map<Id, AggregateResult>([SELECT AssigneeId Id FROM PermissionSetAssignment
   WHERE AssigneeId = :addIds AND PermissionSetId = :pereset.Id GROUP BY AssigneeId]).keySet());

for(Id userId: addIds) {
    permissionSetList.add(new PermissionSetAssignment(PermissionSetId = pereset.id, AssigneeId = userId));
}
upsert permissionSetList;
delete [SELECT Id FROM PermissionSetAssignment WHERE AssigneeId =:removeIds AND PermissionSetId =:pereset.Id];

@isTest
public class Test_AssignPermissionSet {
public static testmethod void userTest(){
    // This code runs as the Standard User
    Profile profileId = [SELECT Id FROM Profile WHERE Name = 'Standard User' LIMIT 1];
    //User role creation
    UserRole r = new UserRole(DeveloperName = 'MyCustomRole', Name ='System Administrator');
    insert r;
    // Perform user data preparation.
    User usr = new User(LastName = 'TestAssignmentUser',
                        FirstName='TestAssignUser',
                        Alias = 'Test',
                        Email = 'Test@gmail.com',
                        Username = 'testAssign@gmail.com',
                        ProfileId = profileId.id,
                        TimeZoneSidKey = 'GMT',
                        LanguageLocaleKey = 'en_US',
                        EmailEncodingKey = 'UTF-8',
                        LocaleSidKey = 'en_US',
                        UserRoleId = r.Id
                       );
    // Start the test, this changes governor limit context to
    test.startTest();
    // Insert the user records that cause the trigger to execute.
    insert usr;
    PermissionSetAssignment per=[select PermissionSetId,PermissionSet.Name,PermissionSet.label,AssigneeId from PermissionSetAssignment where Assignee.Id =:usr.id limit 1];
    // Comparing Permission set userId with Inserted UserId
    // This indicates Permission set created for that Inserted User
    system.assertEquals(usr.Id,per.AssigneeId);
    PermissionSet permission=[SELECT Name,Label FROM PermissionSet where id=:per.PermissionSetId];
    system.assertEquals('SBU Impact Visible',permission.Label);
    // Stop the test, this changes limit context back to test from trigger.
    test.stopTest();
}}

trigger AssignPermissionSet on User (after insert, after Update) {
    PermissionSet pereset = [SELECT Id FROM PermissionSet WHERE Label ='SBU Impact Visible'];

    Set<Id> addIds = new Set<Id>();
    Set<Id> removeIds = new Set<Id>();
    Set<Id> roleIds = new Map<Id, UserRole>([
        SELECT Id
        FROM UserRole
        WHERE Name LIKE '%E&C%' OR Name LIKE '%Commerical Ops%' OR Name LIKE '%Energy & Chemicals%' OR Name LIKE '%All Fluor%'OR Name LIKE '%System Administrator%'
    ]).keySet();

    for(User record : Trigger.new) {
        if(record.IsActive && roleIds.contains(record.UserRoleId)) {
            addIds.add(record.Id):
        }
        else {
            removeIds.add(record.Id):
        }
    }

    PermissionSetAssignment[] permissionSetList = new PermissionSetAssignment[0];
    addIds.removeAll(new Map<Id, AggregateResult>([SELECT AssigneeId Id FROM PermissionSetAssignment WHERE AssigneeId = :addIds AND PermissionSetId = :pereset.Id GROUP BY AssigneeId]).keySet());

    for(Id userId: addIds) {
        permissionSetList.add(new PermissionSetAssignment(PermissionSetId = pereset.id, AssigneeId = userId));
    }

    upsert permissionSetList;

    delete [SELECT Id FROM PermissionSetAssignment WHERE AssigneeId =:removeIds AND PermissionSetId =:pereset.Id];
}

@IsTest
public class Test_AssignPermissionSet {

    @IsTest
    public static void when_user_is_inserted_then_assign_permission_set(){
        Profile profileId = [SELECT Id FROM Profile WHERE Name = 'Standard User' LIMIT 1];
        UserRole r = new UserRole(DeveloperName = 'MyCustomRole', Name ='System Administrator');
        insert r;

        User usr = new User(LastName = 'TestAssignmentUser',
                            FirstName='TestAssignUser',
                            Alias = 'Test',
                            Email = 'Test@gmail.com',
                            Username = 'testAssign@gmail.com',
                            ProfileId = profileId.id,
                            TimeZoneSidKey = 'GMT',
                            LanguageLocaleKey = 'en_US',
                            EmailEncodingKey = 'UTF-8',
                            LocaleSidKey = 'en_US',
                            UserRoleId = r.Id
                        );

        Test.startTest();
        insert usr;
        Test.stopTest();

        // Comparing Permission set userId with Inserted UserI. This indicates Permission set created for that Inserted User
        PermissionSetAssignment per = [SELECT PermissionSetId, PermissionSet.Name, PermissionSet.label, AssigneeId FROM PermissionSetAssignment WHERE Assignee.Id = :usr.id LIMIT 1];
        PermissionSet permission = [SELECT Name, Label FROM PermissionSet WHERE Id = :per.PermissionSetId];
        System.assertEquals(usr.Id,per.AssigneeId);
        System.assertEquals('SBU Impact Visible',permission.Label);
    }