I initiated an extensive user research and testing program. I spoke to hundreds of people during a crypto craze, and built out personas when very little info existed. These were originally published on uxdesign.cc. Several crypto firms reached out after publication. I maintain an active interest in the world of cryptocurrency.
Problem
We don't know who the user is, and we are not validating our designs early enough.
Solution
I built a full “user testing lab” from scratch. I evolved a series of personas out of this research. Valuable insights were gleaned, which led to direct changes in the app.
I wrote about how to conduct mobile user testing for UX Collective here
(I think it's the best guide written on the topic...)

The Personas
One-page Infographic

Mobile User Testing
In order to validate our designs, I bought test phones and built special camera sleds for them. I eventually trained a small team of colleagues how to use the equipment, wrote interview scripts, and conducted multiple user test sessions at a week-long conference.
Building a Test Phone
I am quite proud to have engineered a usability testing sled for a growing startup. After fine-tuning the setup and testing with dozens of users, I wrote up everything I had learned for uxdesign.cc. This covers equipment, software, and interview technique.
My case study on mobile user testing was published by UX Collective
Here is a brief gallery, showing how the rig was built and used.
I've also included a video we shot for Pillar, in which I talk about testing the Pillar Wallet.