What is the purpose and importance of test plans in software testing?

Test plan is the project plan for the testing work to be done. It is not a test design specification, a collection of testcases or a set of test procedures; in fact, most of our test plans do not address that level of detail. Many people have different definitions for test plans.

Purpose  of writing Test Plan:-

1)First, by writing a test plan it guides our thinking.  Writing a test plan forces us to confront the challenges that await us and focus our thinking on important topics.

  2)Second, the test planning process and the plan itself serve as the means of communication with other members of the project team, testers, peers, managers and other stakeholders. This communication allows the test plan to influence the project team and the project team to influence the test plan, especially in the areas of organization-wide testing policies and motivations; test scope, objectives and critical areas to test; project and product risks, resource considerations and constraints; and the testability of the item under test.As the project evolves and situations change, we adapt our plans. By updating the plan at major milestone helps us to keep testing aligned with project needs. As we run the tests, we make final adjustments to our plans based on the results. You might not have the time – or the energy – to update your test plans every time a change is made in the project, as some projects can be quite dynamic.

At times it is better to write multiple test plans in some situations. For example, when we manage both integration and system test levels, those two test execution periods occur at different points in time and have different objectives. For some systems projects, a hardware test plan and a software test plan will address different techniques and tools as well as different audiences. However, there are chances that these test plans can get overlapped, hence, a master test plan should be made that addresses the common elements of both the test plans can reduce the amount of redundant documentation.