e2e: add a test for `context ls`

I'm about to refactor the code which includes the Kubernetes support in a way
which relies on something vendoring `./cli/context/kubernetes/` in order to
trigger the inclusion of support for the Kubernetes endpoint in the final
binary.

In practice anything which is interested in Kubernetes must import that package
(e.g. `./cli/command/context.list` does for the `EndpointFromContext`
function). However if it was somehow possible to build without that import then
the `KUBERNETES ENDPOINT` column would be mysteriously empty.

Out of an abundance of caution add a specific check on the final binary.

Signed-off-by: Ian Campbell <ijc@docker.com>
(cherry picked from commit d5d693aa6e)
Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>

e2e/context/context_test.go

@@ -0,0 +1,21 @@
+package context
+
+import (
+	"testing"
+
+	"gotest.tools/golden"
+	"gotest.tools/icmd"
+)
+
+func TestContextList(t *testing.T) {
+	cmd := icmd.Command("docker", "context", "ls")
+	cmd.Env = append(cmd.Env,
+		"DOCKER_CONFIG=./testdata/test-dockerconfig",
+		"KUBECONFIG=./testdata/test-kubeconfig",
+	)
+	result := icmd.RunCmd(cmd).Assert(t, icmd.Expected{
+		Err:      icmd.None,
+		ExitCode: 0,
+	})
+	golden.Assert(t, result.Stdout(), "context-ls.golden")
+}

e2e/context/main_test.go

@@ -0,0 +1,17 @@
+package context
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/docker/cli/internal/test/environment"
+)
+
+func TestMain(m *testing.M) {
+	if err := environment.Setup(); err != nil {
+		fmt.Println(err.Error())
+		os.Exit(3)
+	}
+	os.Exit(m.Run())
+}

e2e/context/testdata/context-ls.golden

@@ -0,0 +1,3 @@
+NAME                DESCRIPTION                               DOCKER ENDPOINT               KUBERNETES ENDPOINT            ORCHESTRATOR
+default *           Current DOCKER_HOST based configuration   unix:///var/run/docker.sock   https://someserver (zoinx)     swarm
+remote              my remote cluster                         ssh://someserver              https://someserver (default)   kubernetes

e2e/context/testdata/test-dockerconfig/config.json

@@ -0,0 +1,7 @@
+{
+	"auths": {},
+	"HttpHeaders": {
+		"User-Agent": "Docker-Client/19.09.0-dev (linux)"
+	},
+	"credsStore": "secretservice"
+}

e2e/context/testdata/test-dockerconfig/contexts/meta/b71199ebd070b36beab7317920c2c2f1d777df8d05e5527d8458fda57cb17a7a/meta.json

@@ -0,0 +1 @@
+{"Name":"remote","Metadata":{"Description":"my remote cluster","StackOrchestrator":"kubernetes"},"Endpoints":{"docker":{"Host":"ssh://someserver","SkipTLSVerify":false},"kubernetes":{"Host":"https://someserver","SkipTLSVerify":false,"DefaultNamespace":"default","Exec":{"command":"heptio-authenticator-aws","args":["token","-i","eks-cf"],"env":null,"apiVersion":"client.authentication.k8s.io/v1alpha1"}}}}

e2e/context/testdata/test-kubeconfig

@@ -0,0 +1,20 @@
+apiVersion: v1
+clusters:
+- cluster:
+    certificate-authority-data: dGhlLWNh
+    server: https://someserver
+  name: test-cluster
+contexts:
+- context:
+    cluster: test-cluster
+    user: test-user
+    namespace: zoinx
+  name: test
+current-context: test
+kind: Config
+preferences: {}
+users:
+- name: test-user
+  user:
+    client-certificate-data: dGhlLWNlcnQ=
+    client-key-data: dGhlLWtleQ==