In any company.. 1st wil be test policy under test policy test strategy will come under test strategy .. test plan wil come.. test plan wil be dynamic prepared by the test lead .. but test strategy will be static.. prepared by the company management..Both Test Strategy and Test Approach both are same. This is prepared by the Project Manager or Test Manager (If he is available). This documents specifies the what are all the testing approach to be followed by the Test Engineers in the Testing Team. This includes:Test Responsibility Matrix (TRM) (Covers the testing topics to be covered in this project)How to communicate with the Test Engineers in a team and Status ReportsDefect Report and Tracking, etc.... Where as Test Plan means: Way of the Test Engineers to be following the Test Approach or Test Methodology to accomplish the Testing. Generally this is prepared by the Test Lead. This includes...Features to be tested and not to be testedWhen to start testingWhen to Suspend testingwhen to stop testingSchedule to accomplish the testing, etc...
Test Plan is a detailed procedure to organize and execute the workflow of a software testing project
Test approach ans test strategy are same,which are included in Test plan
Test methodology document will contain the phases of testing and the test levels that the testing cycle will go through.
So test plan is the Master document which mentions the test approach ,and test methodology in it.