I have a class that encapsulates the results of a scientific measurement. I’m building in unit tests from the beginning, but I don’t have a lot of experience with unit testing and I’m not sure which behaviors I should be testing and how.
My class does three kinds of things:
- Reads measurement data from a file (or a string) into its instance variables
- Writes its measurement data out to a file or a string
- Performs calculations on its data (e.g. getting the average of a set of numbers)
My approach right now is to include a known-good example data file in my
test directory. One test reads the data in from the file, passes it to my class, and makes sure that it meets some basic sanity checks. Another test passes the file’s filename to my class, lets the class read it, and runs the same tests. The remainder of the tests read the data in from the file, pass it to my class, and check that the results of the data-processing methods are correct, given what I know about that data set.
This seems pretty tangled, though. The tests that check (3) implicitly assume that the behaviors of (1) are correct, since it’s the functions in (1) that are being used to populate the class in the first place. And the tests of (1) could benefit from the extensive checks done by the tests for (3). Am I structuring my unit tests poorly, or is this just a natural result of the fact that I need to use a specific dataset in my tests?