There are many steps to designing a pattern. There are the obvious ones, like brainstorming, swatching possible stitches, calculating the sizes/sts/etc. One of the last steps in design is called test knitting.
When the designer has finished the sample, graded the full pattern, written the entire pattern, and also had it tech edited (more about this in another post), they then need to get it test knitted. Knitters can sign up to receive the designer pattern for free in exchange for knitting a full sample and making sure the pattern works for readers. This is a crucial step to make sure that there are no areas that are too difficult for readers to understand the meaning, find any errors that were missed in tech editing, and also show that the pattern does what it says it is going to do.
The test knitter does not need to worry about calculations, fixing pattern problems, etc, all they need to do is knit a sample, following the pattern, and let the designer know any comments/concerns/questions that they have. The designer will re-work any problematic areas, and give help and feedback to the testers. It is a really fun way to work personally with your favorite designers if you get the chance to test for them!
Interested? Here are a few places to look for test knits you can sign up for:
You can also find testing groups on Ravelry for specific designers. Following designers on social media is another great way to find testing calls for specific designers as well, since we usually make it public information when a test is coming up.