Adding unit tests to an existing project

Question

My question is quite relevant to something asked before but I need some practical advice.

I have "Working effectively with legacy code" in my hands and I 'm using advice from the book as I read it in the project I 'm working on. The project is a C++ application that consists of a few libraries but the major portion of the code is compiled to a single executable. I 'm using googletest for adding unit tests to existing code when I have to touch something.

My problem is how can I setup my build process so I can build my unit tests since there are two different executables that need to share code while I am not able to extract the code from my "under test" application to a library. Right now I have made my build process for the application that holds the unit tests link against the object files generated from the build process of the main application but I really dislike it. Are there any suggestions?

Answer 1

Working Effectively With Legacy Code is the best resource for how to start testing old code. There are really no short term solutions that won't result in things getting worse.

Answer 2

I personally would continue doing as you are doing or consider having a build script that makes the target application and the unit tests at the same time (two resulting binaries off the same codebase). Yes it smells fishy but it is very practical.

Kudos to you and good luck with your testing.

Answer 3

I prefer one test executable per test. This enables link-time seams and also helps allow TDD as you can work on one unit and not worry about the rest of your code.

I make the libraries depend on all of the tests. Hopefully this means your tests are only run when the code actually changes.

If you do get a failure the tests will interrupt the build process at the right place.

Answer 4

I'll sketch out a makefile structure you can use:

all: tests executables

run-tests: tests
    <commands to run the test suite>

executables: <file list>
    <commands to build the files>

tests: unit-test1 unit-test2 etc

unit-test1: ,files that are required for your unit-test1>
    <commands to build unit-test1>

That is roughly what I do, as a sole developer on my project

Answer 5

If your test app is only linking the object files it needs to test then you are effectively already treating them as a library, it should be possible to group those object files into a separate library for the main and the test app. If you can't then I don't see that what you are doing is too bad an alternative.

If you are having to link other object files not under test then that is a sign of dependencies that need to be broken, for which you have the perfect book. We have similar problems and use a system like the one suggested by Vlion