🌱 Implement a smoke test for clusterctl plugins

cmd/clusterctl/cmd/plugin_test.go

@@ -0,0 +1,101 @@
+/*
+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"
+	"testing"
+
+	. "github.com/onsi/gomega"
+)
+
+var baseArgs = []string{"clusterctl", "foo"}
+
+const (
+	forkEnvVar          = "CLUSTERCTL_PLUGIN_TEST_FORK"
+	pluginCommandEnvVar = "CLUSTERCTL_PLUGIN_COMMAND"
+)
+
+func Test_plugin(t *testing.T) {
+	// If CLUSTERCTL_PLUGIN_TEST_FORK is set then just execute the command.
+	if os.Getenv(forkEnvVar) != "" {
+		os.Args = append(baseArgs, os.Getenv(pluginCommandEnvVar))
+		Execute()
+		return
+	}
+	g := NewWithT(t)
+	tmpDir := t.TempDir()
+
+	// Create a bash based plugin used for the test which gets added to the PATH variable.
+	pluginPath := filepath.Join(tmpDir, "clusterctl-foo")
+	pathVar := os.Getenv("PATH")
+	g.Expect(os.WriteFile(pluginPath, []byte(pluginCode), 0755)).To(Succeed()) //nolint:gosec
+
+	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",
+		},
+	}
+	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, pathVar))
+			g.Expect(err).To(Succeed())
+			g.Expect(stdout).To(ContainSubstring(tc.expected))
+		})
+	}
+}
+
+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
+}