Chatter Trigger Test Class Missing ParentId

Question

We created a trigger for Chatter. When a post contains the keyword "legal", a new record under ChatterPost will be generated. We also created a Test class but got error. Since we're rather new to trigger, don't know how to fix the test class, please help, thank you so much.

Error Message System.DmlException: Insert failed. First exception on row 0; first error: REQUIRED_FIELD_MISSING, Required fields are missing: [ParentId]: [ParentId] Stack Trace Class.ChatterPostTest.insertNewChatterPostTest: line 9, column 1

Test

@isTest
public class ChatterPostTest
{
    static testMethod void insertNewChatterPostTest()
    {
        Test.StartTest();
        FeedItem f = new FeedItem();
        f.Body = 'legal test';
        insert f;
        Test.StopTest();
        System.assertEquals ('legal test', f.body);
    }
}

Trigger

Trigger ChatterKeywordLegal on FeedItem (after insert) {
    List<FeedItem> FeedItems = new List<FeedItem>();
   for (FeedItem f : Trigger.new) {
           if (f.body!=null &&   f.body.contains('legal' ) ) {
               ChatterPost__c C = new ChatterPost__c();
               c.Description__c = f.body;                   
              insert C;
        }
    }

Answer 1

As the error states, you're missing a field. You need to specify a ParentId value before attempting to insert the FeedItem. That would go in your test method like so:

f.ParentId = UserInfo.getUserId(); // Associate to the current user
insert f;

You'll want to read more about FeedItem to see if there's any other fields you'll need to specify.