Pre-conference workshop given by Markus Schirp at wroclove.rb 2019, the day before his 'Mutant on steroids' talk. Participants exercised mutation testing on small, non-mature subjects — including a 'range example' whose first step used a no-op error to demonstrate that Mutant emits that signal when the initial tests do not pass. The workshop also showed auto-color replacement in action (e.g. < becoming <=, && inverting). The talk the next day skipped most examples to establish nomenclature and point back to the workshop content.