Abstract randReader to fix a test data-race

js/modules/k6/crypto/crypto.go

@@ -30,7 +30,8 @@ type (
 
 	// Crypto represents an instance of the crypto module.
 	Crypto struct {
-		vu modules.VU
+		randReader func(b []byte) (n int, err error)
+		vu         modules.VU
 	}
 )
 
@@ -47,7 +48,7 @@ func New() *RootModule {
 // NewModuleInstance implements the modules.Module interface to return
 // a new instance for each VU.
 func (*RootModule) NewModuleInstance(vu modules.VU) modules.Instance {
-	return &Crypto{vu: vu}
+	return &Crypto{vu: vu, randReader: rand.Read}
 }
 
 // Exports returns the exports of the execution module.
@@ -78,7 +79,7 @@ func (c *Crypto) randomBytes(size int) (*goja.ArrayBuffer, error) {
 		return nil, errors.New("invalid size")
 	}
 	bytes := make([]byte, size)
-	_, err := rand.Read(bytes)
+	_, err := c.randReader(bytes)
 	if err != nil {
 		return nil, err
 	}

js/modules/k6/crypto/crypto_test.go

@@ -2,7 +2,6 @@ package crypto
 
 import (
 	"context"
-	"crypto/rand"
 	"errors"
 	"fmt"
 	"testing"
@@ -74,13 +73,23 @@ func TestCryptoAlgorithms(t *testing.T) {
 	t.Run("RandomBytesFailure", func(t *testing.T) {
 		t.Parallel()
 
-		rt := makeRuntime(t)
-
-		SavedReader := rand.Reader
-		rand.Reader = MockReader{}
+		rt := goja.New()
+		rt.SetFieldNameMapper(common.FieldNameMapper{})
+
+		m, ok := New().NewModuleInstance(
+			&modulestest.VU{
+				RuntimeField: rt,
+				InitEnvField: &common.InitEnvironment{},
+				CtxField:     context.Background(),
+				StateField:   nil,
+			},
+		).(*Crypto)
+		require.True(t, ok)
+		require.NoError(t, rt.Set("crypto", m.Exports().Named))
+
+		m.randReader = MockReader{}.Read
 		_, err := rt.RunString(`
 		crypto.randomBytes(5);`)
-		rand.Reader = SavedReader
 
 		assert.Error(t, err)
 	})