kubernetes: Kubeadm tests fail when run using go test ./...

What happened: When I do go test ./... from the kubernetes root, it fails because the tests in cmd/kubeadm/test have external dependencies. KUBEADM_PATH is required for example.

...
--- FAIL: TestCmdCompletion (0.00s)
panic: the environment variable KUBEADM_PATH must point to the kubeadm binary path [recovered]
	panic: the environment variable KUBEADM_PATH must point to the kubeadm binary path

goroutine 21 [running]:
testing.tRunner.func1(0xc0000f2400)
	/usr/local/go/src/testing/testing.go:874 +0x3a3
panic(0x1231680, 0x15a2570)
	/usr/local/go/src/runtime/panic.go:679 +0x1b2
k8s.io/kubernetes/cmd/kubeadm/test/cmd.getKubeadmPath(...)
	/home/bpursley/go/src/k8s.io/kubernetes/cmd/kubeadm/test/cmd/util.go:89
k8s.io/kubernetes/cmd/kubeadm/test/cmd.TestCmdCompletion(0xc0000f2400)
	/home/bpursley/go/src/k8s.io/kubernetes/cmd/kubeadm/test/cmd/completion_test.go:22 +0x1f8
testing.tRunner(0xc0000f2400, 0x14a5370)
	/usr/local/go/src/testing/testing.go:909 +0xc9
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:960 +0x350
FAIL	k8s.io/kubernetes/cmd/kubeadm/test/cmd	0.012s
?   	k8s.io/kubernetes/cmd/kubeadm/test/kubeconfig	[no test files]
?   	k8s.io/kubernetes/cmd/kubeadm/test/resources	[no test files]
FAIL

What you expected to happen: The Kubernetes Testing Guide says I should be able to run all unit tests using go test ./...

How to reproduce it (as minimally and precisely as possible): Clone the repository and run go test ./... from the project root.

Or, you can more quickly see the problem if you rjust un that from the cmd/kubeadm subfolder like this:

cd cmd/kubeadm
go test ./...

Anything else we need to know?: make test specifically excludes cmd/kubeadm/test so that the problem does not occur if you use make test.

When this issue is fixed, we should probably remove this exclusion as well.

Environment:

• Kubernetes version (use kubectl version): 1.19 (master branch)
• Cloud provider or hardware configuration: n/a
• OS (e.g: cat /etc/os-release):

NAME="Ubuntu"
VERSION="20.04 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

• Kernel (e.g. uname -a):

Linux cinlogic-xps13 5.4.0-31-generic #35-Ubuntu SMP Thu May 7 20:20:34 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

• Install tools:
• Network plugin and version (if this is a network-related bug):
• Others:

go version go1.13.4 linux/amd64