The idea of one assertion per test is to be testing one thing in each test. That may require one assertion. In your example, each of the three assertions is independent and makes sense to be in a separate test. The clue is that you have clear "business" types names for each test.
Consider this example:
I'm testing one business case/scenario although I happen to use two assertions. I might even refactor the assertions to another method to show they go together.