Hello all,

I have a trigger that one of y'all helped me build (many thanks!). The trigger works perfectly to change the case status when a FeedItem is posted witha  Parent ID of a case where the feed body ends with "Case closed".
As noted, the trigger works fine in the Sandbox, however my Apex Class used for testing is failing due to the following error:
System.QueryException: List has no rows for assignment to SObject

The Apex Trigger is:
trigger UpdateCaseCloseStatus on FeedItem (after insert) {
    
    List<Case> listOfCases = new List<Case>();
    
    for (FeedItem fi : Trigger.new) {
        
        //--- This retrieves the case for which feed has been entered.
        Case c = [select id from Case where Id = :fi.ParentId];

        //--- Now we check if the feed ends with text 'Case Closed'. We are checking case insensitive text.
        if (fi.Body.endsWithIgnoreCase('Case Closed')) {
            c.Status = 'Complete';
        }
        listOfCases.add(c);
    }
    update listOfCases;
}

The Apex Class is:
@isTest
public class TestFeedPost    {
    static testMethod void insertNewFeedPost()     {
        
        FeedItem feedToCreate = new FeedItem();
        
        feedToCreate.ParentId    =       '500q0000001Pavd';
        feedToCreate.Body        =       'Blah blah blah close case';
        feedToCreate.Type        =        'TextPost';
        
        insert feedToCreate;
        }
        }


The full error message is:
<span unselectable="on" "="" style="display: block; padding: 3px 4px; overflow: hidden; margin-left: 0px; color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: 12px; line-height: normal; white-space: nowrap; background-color: rgb(218, 240, 249);">
System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, UpdateCaseCloseStatus: execution of AfterInsert caused by: System.QueryException: List has no rows for assignment to SObject Trigger.UpdateCaseCloseStatus: line 8, column 1: []



Any assistance would be greatly appreciated.

Thanks!