Last September I published an article, entitled Idea Validation - Much more than A/B experiments, in which I explained the concept of validating product ideas systematically through assessment, fact-finding, tests, experiments and releases (AFTER).
The article seemed to have resonated with a lot of people - it became one of my most read and most shared. So I just published a full eBook (46 pages) on the topic - Testing Product Ideas Handbook. The eBook explain the core concepts in more detail: