title: Test dependency not retrieved by `go get`
body: <p>I'm using Golang (1.9 at this time), and using GitLab CI to test and build binaries and Docker containers.</p>
  
  <p>For some projects, I run into this issue (GitLab CI output):</p>
  
  <pre><code>$ go get
  $ go get -u github.com/golang/lint/golint
  $ go tool vet -composites=false -shadow=true *.go
  $ golint ./...
  $ go test --race $(go list ./... | grep -v /vendor/)
  # gitlab.my.site/core/proj/mypkg mypkg/mypkg_test.go:18:2: cannot find package 
  "gitlab.my.site/core/otherproj/otherpkg" in any of:
  /usr/local/go/src/gitlab.my.site/core/otherproj/otherpkg (from $GOROOT)
      /go/src/gitlab.my.site/core/otherproj/otherpkg (from $GOPATH)
  FAIL    gitlab.my.site/core/proj/mypkg [setup failed]
  </code></pre>
  
  <p>The <code>core/otherproj</code> project is private, but clonable through SSH, which is my current workaround.</p>
  
  <p>My main problem is that private projects in dependencies most often work, but sometimes, <code>go get</code>ting them consistently fails.</p>
  
  <p>Worth noting is that the <code>otherproj/otherpkg</code> is only a dependency in the test for <code>proj/mypkg</code>; not its primary functionality.</p>
  
  <p><strong>My question is</strong>; why does this specific dependency not download from <code>go get</code>, and how do I make it download?</p>
  
  <p>Thanks.</p>