Bit of a tangent, though related. It looks like you accidentally stumbled into a version of test driven development ;)
With the big difference obviously being that typically the developer who writes the test also will write the code.
In some situations, this actually makes sense to do with junior developers as part of their training. Where a senior developer sits down with them and write out the tests together, then with the tests as a guide they are thrown into the waters to develop the functionality.
Of course, I suspect that in this case, you were not dealing with a junior. Rather the sort of person who looks at your tests, still is confused and asks for a "quick call" to talk about the tests.
With the big difference obviously being that typically the developer who writes the test also will write the code.
In some situations, this actually makes sense to do with junior developers as part of their training. Where a senior developer sits down with them and write out the tests together, then with the tests as a guide they are thrown into the waters to develop the functionality.
Of course, I suspect that in this case, you were not dealing with a junior. Rather the sort of person who looks at your tests, still is confused and asks for a "quick call" to talk about the tests.