When testing fonts in UI prototyping, you should consider several factors that might influence your font selection and evaluation. For instance, you should test your fonts on different device types and screen sizes that your users might use, such as desktops, laptops, tablets, and smartphones. Additionally, you should evaluate how your fonts adapt to different screen orientations, resolutions, and pixel densities. It is also important to test your fonts in different user scenarios and environments that might affect the readability and attractiveness of your fonts, such as day or night, indoors or outdoors, bright or dim lighting, noisy or quiet surroundings, etc. Moreover, you should consider user characteristics and preferences when testing your fonts with different user segments and personas that might have diverse expectations and needs from your UI. This includes age, gender, education, culture, language, etc. Additionally, you should test how your fonts match your user's moods, emotions, and motivation.