How to generate unit test coverage when using command line flags in Golang subprocess testing?

Question

I have unit tests for most of our code. But I cannot figure out how to generate unit tests coverage for certain code in main() in main package.

The main function is pretty simple. It is basically a select block. It reads flags, then either call another function/execute something, or simply print help on screen. However, if commandline options are not set correctly, it will exit with various error codes. Hence, the need for sub-process testing.

I tried sub-process testing technique but modified code so that it include flag for coverage:

cmd := exec.Command(os.Args[0], "-test.run=TestMain -test.coverprofile=/vagrant/ucover/coverage2.out")

Here is original code: https://talks.golang.org/2014/testing.slide#23 Explanation of above slide: http://youtu.be/ndmB0bj7eyw?t=47m16s

But it doesn't generate cover profile. I haven't been able to figure out why not. It does generate cover profile for main process executing tests, but any code executed in sub-process, of course, is not marked as executed.

I try to achieve as much code coverage as possible. I am not sure if I am missing something or if there is an easier way to do this. Or if it is just not possible.

Any help is appreciated.

Thanks

Amer

Answer 1

I went with another approach which didn't involve refactoring main(): see this commit:

I use a global (unexported) variable:

var args []string

And then in main(), I use os.Args unless the private var args was set:

a := os.Args[1:]
if args != nil {
    a = args
}
flag.CommandLine.Parse(a)

In my test, I can set the parameters I want:

args = []string{"-v", "-audit", "_tests/p1/conf/gitolite.conf"}
main()

And I still achieve a 100% code coverage, even over main().

Answer 2

I would factor the logic that needs to be tested out of main():

func main() {
    start(os.Args)
}

func start(args []string) {
    // old main() logic
}

This way you can unit-test start() without mutating os.Args.

Answer 3

Using @VonC solution with Go 1.11, I found I had to reset flag.CommandLine on each test redefining the flags, to avoid a "flag redefined" panic.:

    for _, check := range checks {
        t.Run("flagging " + check.arg, func(t *testing.T) {
            flag.CommandLine = flag.NewFlagSet(cmd, flag.ContinueOnError)
            args = []string{check.arg}
            main()
        })
    }