refactor and organize code

internal/gperr/utils_test.go

@@ -0,0 +1,58 @@
+package gperr
+
+import (
+	"errors"
+	"testing"
+)
+
+type testErr struct{}
+
+func (e *testErr) Error() string {
+	return "test error"
+}
+
+func (e *testErr) MarshalJSON() ([]byte, error) {
+	return nil, nil
+}
+
+func TestIsJSONMarshallable(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want bool
+	}{
+		{
+			name: "testErr",
+			err:  &testErr{},
+			want: true,
+		},
+		{
+			name: "baseError",
+			err:  &baseError{},
+			want: true,
+		},
+		{
+			name: "nestedError",
+			err:  &nestedError{},
+			want: true,
+		},
+		{
+			name: "withSubject",
+			err:  &withSubject{},
+			want: true,
+		},
+		{
+			name: "standard error",
+			err:  errors.New("test error"),
+			want: false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if got := IsJSONMarshallable(test.err); got != test.want {
+				t.Errorf("IsJSONMarshallable(%v) = %v, want %v", test.err, got, test.want)
+			}
+		})
+	}
+}