write a test class for apex class - apex

Question

I am new to apex, I'm interested in writing a test class for the following controller, but not sure where to begin. Here is my apex class code.
public class tree {
public Account acct{get;set;}
//private final Account acct;
public ApexPages.StandardController stdController {get;set;}
public tree(ApexPages.StandardController stdController) {
stdController.addFields(new String[]{'Id','Tete_de_groupe__c'});
this.acct = (Account)stdController.getRecord();
// this.stdController = stdController;
}
public List<Account> listOfAccount(){
List<Account> acctList;
if (acct.Tete_de_groupe__c == null){
acctList = [SELECT Name,Parent.Name,id,Code_NAF__c ,Industry ,RecordType.Name,Adresse_Agence__c, Tete_de_groupe__c,Statut__c
FROM Account
where id = :this.acct.id or Tete_de_groupe__c = :this.acct.id ];}
else {
acctList = [Select Name,Parent.Name,id,Tete_de_groupe__c,Statut__c
from Account
where id = :this.acct.Tete_de_groupe__c or Tete_de_groupe__c = :this.acct.Tete_de_groupe__c];}
return acctList;
}
Public String getaccountdata(){
String datastr1 = '';
String datastr2 = '';
String datastr = '';
List<Account> lstOfAcc =listOfAccount();
for (integer i=0;i<lstOfAcc.size();i++){
if (lstOfAcc[i].Parent.Name == null){
datastr1 = datastr1 + '{"name": "';
datastr1+= lstOfAcc[i].Name;
datastr1+= '","parent": ';
datastr1+= lstOfAcc[i].Parent.Name;
datastr1+= ',"accountid": "';
datastr1+= lstOfAcc[i].id;
datastr1+= '","Statut__c": "';
datastr1+= lstOfAcc[i].Statut__c;
datastr1+='" }';
}
else{
datastr2 = datastr2 + '{"name": "';
datastr2+= lstOfAcc[i].Name;
datastr2+= '","parent": "';
datastr2+= lstOfAcc[i].Parent.Name;
datastr2+= '","accountid": "';
datastr2+= lstOfAcc[i].id;
datastr2+= '","Statut__c": "';
datastr2+= lstOfAcc[i].Statut__c;
datastr2+='" },';
}
}
if(datastr2 == ''){datastr = '[' + datastr1 + ']';}
else {
datastr2 = datastr2.substring(0,datastr2.length()-1);
datastr = '[' + datastr1 +','+ datastr2 + ']'; }
return datastr;
}
}
I want to create test class. Guys need help if some one can tell me about test class of this apex class.

Answer 1

AParise pointed out the consideration. What you need to do in your test class, step by step:
Insert some account objects into the database (the test runs doesn't see any data by default, and that's OK)
Keep the ID from the first account and use it for Tete_de_groupe__c for the others.
Call the function, roughly like this:
Account mainAccount = populateTestAccounts(); // Helper function
Tree t = new Tree();
t.setAcct(mainAccount);
String result = t.getaccountdata();
assert(....);
That should do the trick!

Answer 2

For unit tests regarding classes like the one you posted, the easiest way is to think about expected results given a code path. For each test method, ask yourself: "Given this set of data, when I invoke this method, I expect this to occur".
Let's walk through your "getaccountdata" method.
"Given this set of data..." - What data does this method require for proper execution? Without diving too deep into your logic, this probably means inserting some Account sObjects.
"When I invoke this method..." - the "getaccountdata" method is being invoked.
"I expect this to occur..." - This is where your assertions come into play. You created the Account sObjects with specific values, so verify that these values propagated into your method return value.