neorpc: ensure errors.Is and errors.As work properly with neorpc.Error

Close #3188.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

pkg/neorpc/errors_test.go

@@ -0,0 +1,35 @@
+package neorpc
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestError_ErrorsAs(t *testing.T) {
+	err := NewInternalServerError("some error")
+	wrapped := fmt.Errorf("some meaningful error: %w", err)
+
+	// Check that Error can be used as a target for errors.As:
+	var actual *Error
+	require.True(t, errors.As(wrapped, &actual))
+	require.Equal(t, "Internal error (-32603) - some error", actual.Error())
+
+	var bad *fs.PathError
+	require.False(t, errors.As(wrapped, &bad))
+}
+
+func TestError_ErrorsIs(t *testing.T) {
+	err := NewInternalServerError("some error")
+	wrapped := fmt.Errorf("some meaningful error: %w", err)
+
+	// Check that Error can be recognized via errors.Is:
+	ref := NewInternalServerError("another server error")
+	require.True(t, errors.Is(wrapped, ref))
+
+	// Invalid target type:
+	require.False(t, errors.Is(wrapped, NewInvalidParamsError("invalid params")))
+}