test(plugin): add comprehensive plugin package tests (#1056)

* test(plugin): add comprehensive plugin package tests

Add tests for Load, FindAll and plugin Exec functionality. Includes test
coverage for plugin loading, discovery and command execution.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

* fix: proper file paths for plugin tests

CacheDirectory() will resolve to current working directory if
pre-defined directory structure is missing.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

---------

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

Author: thevilledev

plugin/install_test.go

@@ -1,6 +1,18 @@
 package plugin
 
-import "testing"
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
 
 func TestIsDirectory(t *testing.T) {
 	testCases := []struct {
@@ -29,3 +41,184 @@ func TestIsDirectory(t *testing.T) {
 		}
 	}
 }
+
+func TestInstall(t *testing.T) {
+	tests := []struct {
+		name             string
+		setup            func(t *testing.T) (source string, wantPluginName string)
+		wantErr          bool
+		wantErrSubstring string
+	}{
+		{
+			name: "install from directory",
+			setup: func(t *testing.T) (string, string) {
+				pluginDir := createInstallTestPlugin(t, "test-plugin")
+				return pluginDir, "test-plugin"
+			},
+			wantErr: false,
+		},
+		{
+			name: "install from valid URL",
+			setup: func(t *testing.T) (string, string) {
+				server := createTestArchiveServer(t, "test-plugin")
+				return fmt.Sprintf("http::%s/plugin.tar.gz?archive=tar.gz", server.URL), "test-plugin"
+			},
+			wantErr: false,
+		},
+		{
+			name: "install from invalid directory",
+			setup: func(_ *testing.T) (string, string) {
+				return "/nonexistent/directory", ""
+			},
+			wantErr: true,
+		},
+		{
+			name: "install from URL with invalid plugin contents",
+			setup: func(t *testing.T) (string, string) {
+				server := createInvalidArchiveServer(t)
+				return fmt.Sprintf("http::%s/invalid.tar.gz?archive=tar.gz", server.URL), ""
+			},
+			wantErr:          true,
+			wantErrSubstring: "loading plugin from dir",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tmpDir := t.TempDir()
+			t.Setenv("XDG_DATA_HOME", tmpDir)
+
+			source, wantPluginName := tt.setup(t)
+			err := Install(context.Background(), source)
+
+			assertError(t, tt.wantErr, tt.wantErrSubstring, err)
+			assertInstallationResult(t, tmpDir, wantPluginName, tt.wantErr)
+		})
+	}
+}
+
+// Helper functions
+func createInstallTestPlugin(t *testing.T, name string) string {
+	t.Helper()
+
+	pluginDir := filepath.Join(t.TempDir(), name)
+	if err := os.MkdirAll(pluginDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	configContent := []byte(fmt.Sprintf(`name: %s
+version: 1.0.0
+command: test-command`, name))
+	if err := os.WriteFile(filepath.Join(pluginDir, "plugin.yaml"), configContent, 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	return pluginDir
+}
+
+func createTestArchiveServer(t *testing.T, pluginName string) *httptest.Server {
+	t.Helper()
+
+	var buf bytes.Buffer
+	gw := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gw)
+
+	configContent := []byte(fmt.Sprintf(`name: %s
+version: 1.0.0
+command: test-command`, pluginName))
+
+	header := &tar.Header{
+		Name: "plugin.yaml",
+		Mode: 0o600,
+		Size: int64(len(configContent)),
+	}
+	if err := tw.WriteHeader(header); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := tw.Write(configContent); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := tw.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := gw.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/x-gzip")
+		_, _ = w.Write(buf.Bytes())
+	}))
+}
+
+func createInvalidArchiveServer(t *testing.T) *httptest.Server {
+	t.Helper()
+
+	var buf bytes.Buffer
+	gw := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gw)
+
+	header := &tar.Header{
+		Name: "dummy.txt",
+		Mode: 0o600,
+		Size: 0,
+	}
+	if err := tw.WriteHeader(header); err != nil {
+		t.Fatal(err)
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := gw.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/x-gzip")
+		_, _ = w.Write(buf.Bytes())
+	}))
+}
+
+func assertError(t *testing.T, wantErr bool, wantMsg string, actual error) {
+	t.Helper()
+
+	if wantErr {
+		if actual == nil {
+			t.Fatal("expected error but got none")
+		}
+		if wantMsg != "" && !strings.Contains(actual.Error(), wantMsg) {
+			t.Errorf("error %q should contain %q", actual.Error(), wantMsg)
+		}
+	} else if actual != nil {
+		t.Fatalf("unexpected error: %v", actual)
+	}
+}
+
+func assertInstallationResult(t *testing.T, tmpDir, wantPluginName string, wantErr bool) {
+	t.Helper()
+
+	if wantErr {
+		assertTempFilesCleaned(t, tmpDir)
+		return
+	}
+
+	pluginDir := filepath.Join(tmpDir, ".conftest", "plugins", wantPluginName)
+	if _, err := os.Stat(pluginDir); os.IsNotExist(err) {
+		t.Errorf("plugin directory %q not found", pluginDir)
+	}
+
+	configPath := filepath.Join(pluginDir, "plugin.yaml")
+	if _, err := os.Stat(configPath); os.IsNotExist(err) {
+		t.Error("plugin.yaml not found in plugin directory")
+	}
+}
+
+func assertTempFilesCleaned(t *testing.T, tmpDir string) {
+	t.Helper()
+
+	matches, _ := filepath.Glob(filepath.Join(tmpDir, ".conftest", "plugins", "conftest-plugin-*"))
+	if len(matches) > 0 {
+		t.Errorf("temporary directories not cleaned up: %v", matches)
+	}
+}