package sources layout has changed from .../src/pkg/PKG_NAME to .../src/PKG_NAME
e.g.
$ withmock go test
ERROR: open /usr/local/Cellar/go/1.4/libexec/src/pkg/net/http: no such file or directory
handle internal package
$ withmock go test
ERROR: Failed to install '_et/http': exit status 1
output:
package _et/http
imports net/http/internal: use of internal package not allowed