Who is normally responsible for the creation and update of a test plan for a project? code example

Example 1: what is test plan

A Test Plan is a detailed document that describes
the test strategy, objectives, schedule, 
estimation, deliverables, and resources
required to perform testing for a software product

Example 2: how to write a test plan

Analyze the product
Design the Test Strategy
Define the Test Objectives
Define Test Criteria
Resource Planning
Plan Test Environment
Schedule & Estimation
Determine Test Deliverables