I can type in uhshdsjk and its accepted as a city
Hi. You are correct. The behavior you're describing is a result of the fact that by inputting text into the "Test" tab, you're side-stepping the speech recognition aspect of a normal interaction with an Alexa skill.
If you were to instead speak to your Alexa skill by enabling the microphone on the Test tab, you would likely either see a slot value representing a best effort guess, or no slot value at all.