Testing for large language model (LLM) applications presents unique challenges due to their non-deterministic outputs, which differ from traditional software testing that relies on predictable outcomes. This practical guide introduces automated testing strategies for LLM applications by utilizing datasets and experiment runners, inspired by Hamel Husain's framework. It distinguishes between testing and evaluation, emphasizing that testing involves running checks for pass/fail results, while evaluation measures model quality on a continuous scale. The guide demonstrates how to implement these tests using Langfuse's Experiment Runner SDK, focusing on a geography question-answering system. It explains the use of datasets for input/output pairs, experiment runners to execute applications, and evaluators to score outputs based on criteria like accuracy. This testing approach serves as automated regression tests, ensuring LLM applications maintain quality as changes are made. The guide also covers integrating tests into continuous integration pipelines and using remote datasets with LLM-as-a-judge evaluators for more sophisticated evaluations.