don't run main function when testing (fixes #277)

[neelance]

No description provided.

[dmitshur]

I can confirm this fixes the reproduce case I've provided.

[dmitshur]

If it's not too hard, it might be nice to add a regression test for this, since in most cases running main() during a test may not be as immediately obvious but lead to strange side-effects.

Feel free to use or base it on github.com/shurcooL/play/145 if that's helpful.

If you feel confident this won't break in the future or this test doesn't belong here, it's fine not to add it.

[dmitshur]

I am not familiar with the context of the fix, and I don't completely understand the change, so take that into account.

I don't see anything obviously wrong with it, tests pass and the reported issue is resolved, so it LGTM but I cannot offer full confidence in it.

[neelance]

Test added.

Can I tell you more about the change? The problem was that I assumed that you can not depend on a main package, which is usually the case. Only that testing creates an additional fake main package which depends on the main package being tested. The $init function or a package used to also run the main function and this needs to stay there because of code that needs to be generated to support blocking init functions. So the solution that I chose is to store the package that needs to run the main function in the global $mainPkg variable and add an if statement around the call to main that checks if the current package being initialized is really the correct main package.

[dmitshur]

That was very helpful indeed, thanks for the explanation.

[dmitshur]

@neelance, are you aware that this name TestMain has special meaning as of Go 1.4?

The testing package has a new facility to provide more control over running a set of tests. If the test code contains a function

func TestMain(m *testing.M) 

that function will be called instead of running the tests directly. The M struct contains methods to access and run the tests.

Source: https://golang.org/doc/go1.4

I kinda suspect it's an unintentional usage of that feature here, since you're testing a feature named main. If so, I think it's better we rename it to avoid doing something unintentionally just due to a coincidence in naming, as it might cause confusion later (if other tests are ever added here, they will not run). Perhaps func TestNotRunMain(m *testing.M) or so?

[dmitshur]

@neelance, did you see this?

[neelance]

I did not know that. Thanks for pointing it out. Fixed via 01e6396.

[dmitshur]

Great, thanks!