Tests are run twice for hybrid _test packages

[Invertisment]

Golang allows placing two packages into one folder if one of them has _test suffix.
It runs normally for default kind of tests but when I try to use gocheck in the same manner my tests get run twice.

I've created a sample repository for this bug:
https://github.com/Invertisment/gocheck-test-package-bug

This is the output of my test suite:

go test -v ./...
=== RUN   Test
OK: 1 passed
--- PASS: Test (0.00s)
PASS
ok  	_____/double-test/gocheck_one_package	0.010s
=== RUN   Test
OK: 2 passed
--- PASS: Test (0.00s)
=== RUN   Test
OK: 2 passed
--- PASS: Test (0.00s)
PASS
ok  	_____/double-test/gocheck_two_packages_one_folder	0.007s
=== RUN   TestOnePackage
--- PASS: TestOnePackage (0.00s)
PASS
ok  	_____/double-test/one_package	0.009s
=== RUN   TestTwoInOneMain
--- PASS: TestTwoInOneMain (0.00s)
=== RUN   TestTwoInOneTestPackage
--- PASS: TestTwoInOneTestPackage (0.00s)
PASS
ok  	_____/double-test/two_packages_one_folder	0.001s

[robert-zaremba]

Hi, I've sold this problem in the following PR:
Invertisment/gocheck-test-package-bug#1

You can find a reason of the double test run in the commit description. Basically gocheck test registration (TestingT) was run twice.