In a service company scenario you do not own the source code under any circumstances nor the test (plans/scenarios/cases ) etc. You do it for a client who has outsourced these jobs to you. The ownership for all this eventually lies with the client and you have to share it back with him. This will be dependent on the statement of work agreement with the client.
In a product company scenario, source code along with all test related documentation is owned by the company itself. They may or may not share it with the customer of the product. Sharing will be highly dependent on the business need.