Szymon Fiedler Senior Software Engineer building systems that scale. Domain-Driven Design practitioner, Rails Event Store maintainer, event sourcing expert. I specialize in the complex intersection of money, compliance and legacy code. I'm a member of the Arkency team. https://speakerdeck.com/szymonfiedler 2014-03-31 05:22:03 -0400 Would your test catch this bug? A mutation testing story 20 minute long variant of the talk, given at Paris.rb meetup 2026-05-05 20 minute long variant of the talk, given at Paris.rb meetup 2026-05-05 Tue, 05 May 2026 00:00:00 -0400 https://speakerdeck.com/szymonfiedler/would-your-test-catch-this-bug-a-mutation-testing-story https://speakerdeck.com/szymonfiedler/would-your-test-catch-this-bug-a-mutation-testing-story Would Your Tests Catch This Bug? A mutation testing story Your tests pass, but do they actually test anything? With AI agents now writing tests, mutation testing becomes critical. Learn how Mutant exposes gaps in your test coverage by introducing bugs. If tests still pass, you’ve found a blind spot. Real code. Real mutations. Real insights. RBQConf — Austin, TX 26-27.03.2026 Your tests pass, but do they actually test anything? With AI agents now writing tests, mutation testing becomes critical. Learn how Mutant exposes gaps in your test coverage by introducing bugs. If tests still pass, you’ve found a blind spot. Real code. Real mutations. Real insights. RBQConf — Austin, TX 26-27.03.2026 Fri, 27 Mar 2026 00:00:00 -0400 https://speakerdeck.com/szymonfiedler/would-your-tests-catch-this-bug-a-mutation-testing-story https://speakerdeck.com/szymonfiedler/would-your-tests-catch-this-bug-a-mutation-testing-story Rewrite with confidence: validating business rules through isolated testing EuRuKo 2025, Viana Do Castelo, Portugal EuRuKo 2025, Viana Do Castelo, Portugal Thu, 18 Sep 2025 00:00:00 -0400 https://speakerdeck.com/szymonfiedler/rewrite-with-confidence-validating-business-rules-through-isolated-testing https://speakerdeck.com/szymonfiedler/rewrite-with-confidence-validating-business-rules-through-isolated-testing Speaker's delight Sat, 12 Apr 2025 00:00:00 -0400 https://speakerdeck.com/szymonfiedler/speakers-delight https://speakerdeck.com/szymonfiedler/speakers-delight Ruby 3.2 features you probably haven't used yet Thu, 23 Nov 2023 00:00:00 -0500 https://speakerdeck.com/szymonfiedler/ruby-3-dot-2-features-you-probably-havent-used-yet https://speakerdeck.com/szymonfiedler/ruby-3-dot-2-features-you-probably-havent-used-yet Form objects done right How to use form objects in ruby without breaking single responsibility principle. Video from talk: https://www.youtube.com/watch?v=i90j94Eu8LM How to use form objects in ruby without breaking single responsibility principle. Video from talk: https://www.youtube.com/watch?v=i90j94Eu8LM Thu, 27 Mar 2014 00:00:00 -0400 https://speakerdeck.com/szymonfiedler/form-objects-done-right https://speakerdeck.com/szymonfiedler/form-objects-done-right