Test Scope - The Goal of Isolation

In isolation, it's important to ensure the reliability of the test that no matter when and how we run the test will always get the same result. The smaller the test scope like in unit test, we tend to test more technical things,. But they are very fast and if they fail, they tell you exactly where the problem is. If we take a step back and think about where I might test my application, do I run my tests at the API layer? What are the options that are available for those kind of tests?"