diff --git a/pkg/node/protocol_test.go b/pkg/node/protocol_test.go
index 1d728a4..c20c5c2 100644
--- a/pkg/node/protocol_test.go
+++ b/pkg/node/protocol_test.go
@@ -1,7 +1,6 @@
 package node
 
 import (
-	"fmt"
 	"testing"
 )
 
@@ -153,8 +152,14 @@ func TestConvenienceFunctions(t *testing.T) {
 	}
 }
 
+// testErr is a plain error type used to verify behaviour with non-ProtocolError values.
+// err := &testErr{"context: operation failed"}
+type testErr struct{ message string }
+
+func (e *testErr) Error() string { return e.message }
+
 func TestGetProtocolErrorCode_NonProtocolError(t *testing.T) {
-	err := fmt.Errorf("regular error")
+	err := &testErr{"regular error"}
 	if GetProtocolErrorCode(err) != 0 {
 		t.Error("Expected 0 for non-ProtocolError")
 	}