Simple question about inducing errors for os.Setenv() and os.Unsetenv()

I'm trying to figure out how too make os.Setenv() and os.Unsetenv() fail so I can write a _test.go around some code which calls these. I want to be complete and test the failure conditions.

Of course, the signatures are: func Setenv(key, value string) error and func Unsetenv(key) error

I looked thru the source code and they had tests, but it doesn't look like they had a test where these failed.

Yeah, I could just ignore the error return, but that kinda defeats having an error return.
So, anyone have a lead to how to make these fail?

Thanks in advance...

os.Setenv is a very thin wrapper around syscall.Setenv, and simply returns whichever error syscall.Setenv returns, wrapped with NewSyscallError.

The error cases are evident in the source, which is only 18 lines long:

func Setenv(key, value string) error {
	envOnce.Do(copyenv)
	if len(key) == 0 {
		return EINVAL
	}
	for i := 0; i < len(key); i++ {
		if key[i] == '=' || key[i] == 0 {
			return EINVAL
		}
	}
	// On Plan 9, null is used as a separator, eg in $path.
	if runtime.GOOS != "plan9" {
		for i := 0; i < len(value); i++ {
			if value[i] == 0 {
				return EINVAL
			}
		}
	}
}

So to provoke an error, you need to satisfy any of the following:

• len(key) == 0
• key[i] == '=' || key[i] == 0
• runtime.GOOS != "plan9" and value[i] == 0

syscall.Unsetenv on the other hand never returns an error, it can only return nil.

func Unsetenv(key string) error {
	envOnce.Do(copyenv)

	envLock.Lock()
	defer envLock.Unlock()

	if i, ok := env[key]; ok {
		envs[i] = ""
		delete(env, key)
	}
	unsetenv_c(key)
	return nil
}

I would speculate that it is written as returning an error for consistency with the Setenv, and to provide support for some future platform or environment where it may produce an error under certain conditions.