Test Development Life Cycle

Usually, Testing is considered as a part of the System Development Life Cycle, but it can be also termed as Test Development Life Cycle or Software Testing Life Cycle.
The diagram does not depict where and when you write your Test Plan and Strategy documents. But, it is understood that before you begin your testing activities these documents should be ready. Ideally, when the Project Plan and Project Strategy are being made, this is the time when the Test Plan and Test Strategy documents are also made.

More on phases in Software Test Life Cycle (or Test Development Life Cycle)..