Making the test tool, and some more, your friend
In Chapter 4, The Test Tools, Standard Tests, and Standard Test Libraries, we introduced you to the test tool and we used it frequently during the work we did on the test examples. We applied it to test the test after having inserted a bug to deliberately cause a verification error. Next to VS Code, your coding tool, and debugger, the test tool is one of your best friends. Keep it running while you develop, and do not wait till the code is ready; verify each atomic change by running the tests, as mentioned previously. The goal is to make automated testing part of development.
Create a specific test suite to hold the test codeunits that relate to the code you are working on. In most of your projects, it's very likely, as with the LookupValue extension, that you end up with a bunch of test codeunits that will be executed within less than a minute. While working on a new test codeunit, create a new test suite to only hold that codeunit...