Testing fonts have full character sets and styles, so you can use them in your unpublished comps and get a sense of exactly what each font package contains. There is no time limit on my testing license; I only ask that you return to purchase a full license if you wish to use the fonts in any context other than testing.
You can get a testing license by selecting “Testing” from the “License Type” dropdown on any font’s checkout page, like so:
I also offer my library of fonts on Fontstand, an app that has free trials and inexpensive font rentals.
You are also welcome to inquire about fonts that are not yet released, as I occasionally offer beta licenses for those as well if they are in working condition.