🌱 Implement a smoke test for clusterctl plugins

Author: dmvolod

cmd/clusterctl/cmd/plugin_test.go

@@ -0,0 +1,105 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"testing"
+
+	"github.com/Masterminds/goutils"
+	. "github.com/onsi/gomega"
+)
+
+var baseArgs = []string{"clusterctl", "foo"}
+
+const (
+	forkEnvVar          = "FORK"
+	pluginCommandEnvVar = "PLUGIN_COMMAND"
+)
+
+func Test_plugin(t *testing.T) {
+	if goutils.DefaultString(os.Getenv(forkEnvVar), "false") == strconv.FormatBool(false) {
+		g := NewWithT(t)
+		tt := []struct {
+			name     string
+			command  string
+			expected string
+		}{
+			{
+				name:     "base plugin command test",
+				expected: "I am a plugin named clusterctl-foo",
+			},
+			{
+				name:     "plugin version command test",
+				command:  "version",
+				expected: "1.0.0",
+			},
+		}
+
+		tmpDir := os.TempDir()
+		defer os.Remove(tmpDir)
+
+		pluginPath := filepath.Join(tmpDir, "clusterctl-foo")
+		path := os.Getenv("PATH")
+		g.Expect(os.WriteFile(pluginPath, []byte(pluginCode), 0755)).To(Succeed()) //nolint:gosec
+
+		for _, tc := range tt {
+			t.Run(tc.name, func(t *testing.T) {
+				g := NewWithT(t)
+				stdout, _, err := runForkTest(t.Name(), fmt.Sprintf("%s=%s", pluginCommandEnvVar, tc.command), fmt.Sprintf("PATH=%s:%s", tmpDir, path))
+				g.Expect(err).NotTo(HaveOccurred())
+				g.Expect(stdout).To(ContainSubstring(tc.expected))
+			})
+		}
+
+		return
+	}
+
+	os.Args = append(baseArgs, os.Getenv(pluginCommandEnvVar))
+	Execute()
+}
+
+var pluginCode = `#!/bin/bash
+
+# optional argument handling
+if [[ "$1" == "version" ]]
+then
+echo "1.0.0"
+exit 0
+fi
+
+echo "I am a plugin named clusterctl-foo"
+`
+
+func runForkTest(testName string, options ...string) (string, string, error) {
+	cmd := exec.Command(os.Args[0], "-test.run", testName) //nolint:gosec
+	cmd.Env = append(os.Environ(), fmt.Sprintf("%s=%v", forkEnvVar, true))
+	cmd.Env = append(cmd.Env, options...)
+
+	var stdoutB, stderrB bytes.Buffer
+	cmd.Stdout = &stdoutB
+	cmd.Stderr = &stderrB
+
+	err := cmd.Run()
+
+	return stdoutB.String(), stderrB.String(), err
+}

cmd/clusterctl/cmd/root.go

@@ -218,7 +218,7 @@ func handlePlugins() {
 			case "help", cobra.ShellCompRequestCmd, cobra.ShellCompNoDescRequestCmd:
 				// Don't search for a plugin
 			default:
-				if err := handlePluginCommand(pluginHandler, cmdPathPieces, 0); err != nil {
+				if err = handlePluginCommand(pluginHandler, cmdPathPieces, 0); err != nil {
 					fmt.Fprintf(os.Stderr, "Error: %v\n", err)
 					os.Exit(1)
 				}

go.mod

@@ -54,10 +54,11 @@ require (
 	sigs.k8s.io/yaml v1.4.0
 )
 
+require github.com/Masterminds/goutils v1.1.1
+
 require (
 	cel.dev/expr v0.18.0 // indirect
 	dario.cat/mergo v1.0.1 // indirect
-	github.com/Masterminds/goutils v1.1.1 // indirect
 	github.com/Masterminds/semver/v3 v3.3.0 // indirect
 	github.com/NYTimes/gziphandler v1.1.1 // indirect
 	github.com/ProtonMail/go-crypto v0.0.0-20230217124315-7d5c6f04bbb8 // indirect