How To Understand @TestClass Apex code with List embedded in Map

Question

I am trying to understand this code ,this seems to be a test class,but i am having hard time to understand the code,i know conceptually how List and Map collection works in Sales force,but this seems to be little difficult to understand,

.In brief to me this seems to test a method which browses a list of CollaborationGroupMember. For that, CollaborationGroup has been created and code tried to add one User.

can some one please take some time to make me understand the below code line by line?

Thanks in advance

  @isTest
  public class TestGroupFactory {
    public static Map<CollaborationGroup, List<CollaborationGroupMember>> groupWithMember() {
      CollaborationGroup groupe = new CollaborationGroup(Name = 'Test1', CollaborationType = 'Public');
      insert groupe;
      groupe = [SELECT Id, Name FROM CollaborationGroup WHERE Name = 'Test1'];
      List<User> users = [SELECT Id, Name, Numero_de_plaque__c, SenderEmail
                        FROM User
                        WHERE Name = 'User User'];
       List<CollaborationGroupMember> cgms = new List<CollaborationGroupMember>();
      for (User u : users) {
          CollaborationGroupMember cgm = new CollaborationGroupMember();
          cgm.CollaborationGroupId = groupe.Id;
          cgm.MemberId = u.Id;
          cgms.add(cgm);
       }
       insert cgms;
        return new Map<CollaborationGroup, List<CollaborationGroupMember>>{groupe => cgms};
     }
}

Answer 1

It is technically a test class, but it does not perform any tests. Its purpose is to create test data for other test classes that contain test methods. The reason it has the @isTest annotation is so that it is only accessible in test context and does not count against the total test coverage of the organization.

The method shown creates a Chatter Group and adds Users to the group if they have the name "User User".

The code below inserts the Chatter Group and then retrieves it so the Id is available. I don't think the retrieval is necessary in this instance, but I'd have to test it.

  CollaborationGroup groupe = new CollaborationGroup(Name = 'Test1', CollaborationType = 'Public');
  insert groupe;
  groupe = [SELECT Id, Name FROM CollaborationGroup WHERE Name = 'Test1'];

The next section retrieves the Users (presumably created in another test class)

      List<User> users = [SELECT Id, Name, Numero_de_plaque__c, SenderEmail
                          FROM User
                          WHERE Name = 'User User'];

Then, a list of CollaborationGroupMembers is instantiated. A loop begins that iterates over every User. For each user, a new CollaborationGroupMember is instantiated and added to the list.

  List<CollaborationGroupMember> cgms = new List<CollaborationGroupMember>();
  for (User u : users) {
      CollaborationGroupMember cgm = new CollaborationGroupMember();
      cgm.CollaborationGroupId = groupe.Id;
      cgm.MemberId = u.Id;
      cgms.add(cgm);
   }

The group members are inserted

insert cgms;

The group and group members are added to a map and returned

return new Map<CollaborationGroup, List<CollaborationGroupMember>>{groupe => cgms};