How to cover a catch statement in a test class?

Question

I have a simple after insert trigger which inserts a task when an account is created. I am struggling to cover the catch statement in my test class. Is there a way to cover it?

Apex Trigger

trigger Account on Account (after insert) {
    
   
        AccountTriggerClass.taskInsert(Trigger.new);
    
   
}

Apex Class

public class AccountTriggerClass {
    
    public static void taskInsert(List<Account> acc)
    {
        try{
            List<Task> taskList = new List<Task>();
            for(Account a : acc){
                Task tk = new Task();
                tk.Subject = 'New Task created by after insert';
                tk.WhatId = a.Id;
                taskList.add(tk);
            }
            
            Database.insert(taskList, false);
        }
        catch(exception ex){
            system.debug(ex.getMessage());
        }
    } 
        
    }

Test Class

@isTest
public class AccountTriggerClassTest {
    
    @isTest private static void taskInsertMethod(){
        Account a = new Account();
        a.Name = 'Test Account 2';
        insert a;
    }   
}

Catch not covered:

Answer 1

Aside from the fact you are just writing to debug on an exception which is not best practice ... nor do you have any asserts (also not best practice) you are using a partial success pattern that will not throw a DMLException

Database.insert(taskList, false);

which is normally coded as:

Database.SaveResult[] results = Database.insert(tasklist,false);
for (Database.SaveResult result : results) {
    if (!result.isSuccess()) { do something useful like log to an sobject the errors for later investigation}
}

Otherwise, given that you are creating valid Task objects, you'll never be able to get an exception without catering your test to validation rules on Task.

Trust me, trying to get 100% code coverage for every exception catch block is a fool's errand - especially if you use some standard exception handling that you reuse over and over.

If you want to learn more about sophisticated strategies for mocking exceptions in service layer classes, check out ApexMocks and the doThrowWhen method in this GitHub repo .. but I suspect this is far more than you want to bite off for the example above.