In agile like development, who should write test cases?
Our team has a task system where we post small incremental tasks assigned to each developer.
Each task is developed in its own branch, and then each branch is tested before being merged to the trunk.
My question is: Once the task is done, who should define the test cases that should be done on this task?
Ideally I think the developer of the task himself is best suited for the job, but I have had a lot of resistance from developers who think it's a waste of their time, or that they simply don't like doing it.
The reason I don't like having my QA people do it, is because I don't like the idea of them creating their own work. For example they might leave out things that are simply too much work to test, and they may not know the technical detail that is needed.
But likewise, the down part of developers doing the test cases, is that they may leave out things that they think will break. (even subconsciously maybe)
As the project manager, I ended up writing the test cases for each task myself, but my time is taxed and I want to change this.
Suggestions?
EDIT: By test cases I mean the description of the individual QA tasks that should be done to the branch before it should be merged to the trunk. (Black Box)
Answer
The Team.
If a defect gets to a customer, it is the team's fault, therefore the team should be writing test cases to assure that defects don't reach the customer.
The Project Manager (PM) should understand the domain better than anyone on the team. Their domain knowledge is vital to having test cases that make sense with regard to the domain. They will need to provide example inputs and answer questions about expectations on invalid inputs. They need to provide at least the 'happy path' test case.
The Developer(s) will know the code. You suggest the developer may be best for the task, but that you are looking for black box test cases. Any tests that a developer comes up with are white box tests. That is the advantage of having developers create test cases – they know where the seams in the code are.
Good developers will also be coming to the PM with questions "What should happen when...?" – each of these is a test case. If the answer is complex "If a then x, but if b then y, except on Thursdays" – there are multiple test cases.
The Testers (QA) know how to test software. Testers are likely to come up with test cases that the PM and the developers would not think of – that is why you have testers.