Final answer:
A program passes tests when it successfully executes and passes every test case in the test suite, to ensure the software is free of bugs and performs as expected under all defined scenarios.
Step-by-step explanation:
In the context of software testing and quality assurance, we can say that a program passes tests when it meets the specified requirements and successfully executes all planned test cases without failure. Simply choosing any other option, such as having a good feeling about the program, only passing the most difficult test case, or passing most but not all test cases, is not sufficient for asserting that a program is free of bugs and ready for production. A test suite usually is made up of many individual tests designed to cover a range of possible inputs and use cases. Therefore, the correct answer is:
D. when the program passes every test case
For a program to be considered robust and reliable, it must be shown to work as expected under all defined scenarios covered by the test suite. If any test cases fail, then there's a risk that the program contains bugs or undesired behavior that could lead to failures or issues in production.