First and foremost thing is to make sure that the product meets the client requirements. Without proper test design (test plan, test cases...) it is difficult to make sure that the product is as per the requirement.
Time required for each test iteration also has to be decided prior to the actual testing based on which we can have other judgments like number of resources, release date, cost estimation.....
We need to do white box, performance and database testing too in addition to regular black box testing which requires a well written test case and plan.
There are many other factors which needs a prior decision / agreement with the client like defect tracking tool to be used, review -meetings between testing and development teams, review meetings with client, number of test iterations required, test environment setup requirements..... A proper planning is required to finalize all these things with the client.
Adhoc and exploratory testing can be done only in the later stages and as such have least importance.
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