# Unit Testing for Individual Tools

Unit testing checks that each tool an AI agent uses works as expected when it stands alone. You write small tests that feed the tool clear input and then compare its output to a known correct answer. If the tool is a function that parses dates, you test many date strings and see if the function gives the right results. Good tests cover normal cases, edge cases, and error cases. Run the tests every time you change the code. When a test fails, fix the tool before moving on. This habit keeps bugs from spreading into larger agent workflows and makes later debugging faster.