Having an expected/input output set when writing something like a parser is standard practice. Turning that set into unit tests is worthless for a few reasons.
1: You will design your code to make them all pass. A unit test is useless if it always passes. When your test framework comes back saying x/x (100%) of tests have passed, you are receiving ZERO information as to the validity of your system.
2: You wrote the unit tests with the same assumptions, biases, and limitations as the code they're testing. If you have a fundamental misunderstanding of what the system should do, it will manifest in both the code and the test. This is true of most unit tests - they are tautological.
3: While doing all of the above and achieving almost zero additional utility, you had to fragment your logic in a way that easily yields itself to unit testing. More than likely, that's not the most readable or understandable way said code could have been written. You sacrificed clarity for unit testability. Metrics like test code coverage unintentionally steer developers to writing unreadable tangled code.
The only use case for unit testing here would be if this parser was a component that gets frequently updated by many people or a component that gets implemented anew for different configurations. But at this point i'm just talking about regression testing, and there are many ways to do that other than unit testing.