Add unit tests for stoneerror package

Introduce comprehensive tests for core functionalities including error creation, metadata handling, wrapping, JSON conversion, and type validation. These tests ensure robustness and reliability of the stoneerror package.

error_test.go

@@ -0,0 +1,53 @@
+package stoneerror
+
+import (
+	"errors"
+	"testing"
+)
+
+func Test_StoneErrorWithoutMetadata(t *testing.T) {
+	stoneError := New(1, "test")
+
+	t.Log(stoneError)
+}
+
+func Test_StoneErrorWithMetadata(t *testing.T) {
+	stoneError := New(1, "test").
+		WithMetadata("key", "value").
+		WithMetadata("key2", "value2")
+
+	t.Log(stoneError)
+}
+
+func Test_NormalWrap(t *testing.T) {
+	normalError := errors.New("test")
+	stoneError := Wrap(normalError, 1, "test")
+	t.Log(stoneError)
+}
+
+func Test_StoneWrap(t *testing.T) {
+	originalError := New(1, "test").
+		WithMetadata("key", "value").
+		WithMetadata("key2", "value2")
+	stoneError := Wrap(originalError, 1, "test")
+	t.Log(stoneError)
+}
+
+func Test_ToJSON(t *testing.T) {
+	stoneError := New(1, "test").
+		WithMetadata("key", "value").
+		WithMetadata("key2", "value2")
+	jsonData := stoneError.ToJSON()
+	t.Log(string(jsonData))
+}
+
+func Test_IsStoneError(t *testing.T) {
+	stoneError := New(1, "test").
+		WithMetadata("key", "value")
+
+	if IsStoneError(stoneError) {
+		t.Log("Is stone error")
+	} else {
+		t.Fail()
+	}
+}