Enforce testutils package is only imported by test files outside plug…

…in/evm

plugin/evm/testutils/metrics.go

@@ -10,6 +10,7 @@ import (
 // If the [metrics.Enabled] is already true, nothing is done.
 // Otherwise, it is set to true and is reverted to false when the test finishes.
 func WithMetrics(t *testing.T) {
+	panicIfCallsFromNonTest()
 	if metrics.Enabled {
 		return
 	}

plugin/evm/testutils/testutils.go

@@ -0,0 +1,27 @@
+// Package testutils contains test utilities ONLY to be used outside plugin/evm.
+// The aim is to reduce changes in geth tests by using the utilities defined here.
+// This package MUST NOT be imported by non-test packages.
+
+package testutils
+
+import (
+	"runtime"
+	"strings"
+)
+
+// panicIfCallsFromNonTest should be added at the top of every function defined in this package
+// to enforce this package to be used only by tests.
+func panicIfCallsFromNonTest() {
+	pc := make([]uintptr, 64)
+	runtime.Callers(0, pc)
+	frames := runtime.CallersFrames(pc)
+	for {
+		f, more := frames.Next()
+		if strings.HasPrefix(f.File, "/testing/") || strings.HasSuffix(f.File, "_test.go") {
+			return
+		}
+		if !more {
+			panic("no test file in call stack")
+		}
+	}
+}

plugin/evm/testutils/testutils_test.go

@@ -0,0 +1,81 @@
+package testutils
+
+import (
+	"fmt"
+	"go/parser"
+	"go/token"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestMustNotImport fails if a package in plugin/evm imports the testutils package.
+func TestMustNotImport(t *testing.T) {
+	var evmPackagePaths []string
+	filepath.WalkDir("../", func(path string, d fs.DirEntry, err error) error {
+		if !d.IsDir() {
+			return nil
+		} else if path == "../testutils" {
+			return nil
+		}
+		evmPackagePaths = append(evmPackagePaths, path)
+		return nil
+	})
+
+	for _, packagePath := range evmPackagePaths {
+		packageName := "github.com/ava-labs/subnet-evm/plugin/evm/" + strings.TrimPrefix(packagePath, "../")
+		imports, err := getPackageImports(packagePath)
+		require.NoError(t, err)
+		_, ok := imports["github.com/ava-labs/subnet-evm/plugin/evm/testutils"]
+		assert.Falsef(t, ok, "package %s imports testutils: testutils should only be used outside plugin/evm.", packageName)
+	}
+}
+
+func getPackageImports(packagePath string) (imports map[string]struct{}, err error) {
+	imports = make(map[string]struct{})
+
+	err = filepath.Walk(packagePath, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		} else if path != packagePath && info.IsDir() {
+			return fs.SkipDir
+		} else if !strings.HasSuffix(info.Name(), ".go") {
+			return nil
+		}
+		err = parseImportsFromFile(path, imports)
+		if err != nil {
+			return fmt.Errorf("failed to parse imports: %s", err)
+		}
+		return nil
+	})
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to walk through package files: %v", err)
+	}
+
+	return imports, nil
+}
+
+func parseImportsFromFile(filePath string, imports map[string]struct{}) error {
+	file, err := os.Open(filePath)
+	if err != nil {
+		return fmt.Errorf("failed to open file %s: %v", filePath, err)
+	}
+	defer file.Close()
+
+	node, err := parser.ParseFile(token.NewFileSet(), filePath, file, parser.ImportsOnly)
+	if err != nil {
+		return fmt.Errorf("failed to parse file %s: %v", filePath, err)
+	}
+
+	for _, nodeImport := range node.Imports {
+		imports[strings.Trim(nodeImport.Path.Value, `"`)] = struct{}{}
+	}
+
+	return nil
+}