is there a way to determine which (unit) tests need to run with a given set of changes in my codebase?

To determine which unit tests need to run with a given set of changes in your codebase, you can use several techniques and tools available in Xcode, as discussed in the WWDC sessions:

Test Plans and Filtering: You can create test plans that include specific test targets and filter tests by tags. This allows you to focus on running only the relevant tests for your changes. You can specify which tests to include or exclude by using tags in the test plan editor. This is particularly useful if you have a large test suite and want to run a subset of tests that are most relevant to your changes. Go further with Swift Testing
Test Navigator: The test navigator in Xcode allows you to filter tests by their status or tags. You can focus on tests that have failed or are relevant to the changes you made. This helps in quickly identifying and running the necessary tests without going through the entire suite. Xcode essentials
Code Coverage: Enabling code coverage can help you determine how much of your codebase is executed when running your tests. This can give you insights into which parts of your code are not covered by existing tests and may need additional testing. Xcode essentials
Parameterized Testing: By using parameterized tests, you can run the same test logic with different inputs, which can help in covering more scenarios with fewer test functions. This approach can also help in identifying which specific inputs cause failures, allowing you to focus on those cases. Go further with Swift Testing

These techniques can help streamline your testing process and ensure that you are running the most relevant tests for your code changes.