The speaker talks about observability-driven development with open telemetry. They discuss the pain of testing microservices and the challenges of integration testing with TDD. They propose using distributed traces as test assertions and introduce the concept of observability-driven development. They show a code example of how to use trace test, an open-source tool, for trace-based testing. The speaker emphasizes the benefits of this approach, such as testing against real data and not having to use mocks. They also mention that trace tests can work with any distributed system that has open telemetry instrumentation. At the end of the talk, there is a Q&A session where the speaker answers questions about using trace tests in production and preventing production code from being bloated with instrumentation.