Added unti tests

Author: cmaglie

internal/arduino/builder/internal/preprocessor/ctags_test.go

@@ -0,0 +1,42 @@
+// This file is part of arduino-cli.
+//
+// Copyright 2025 ARDUINO SA (http://www.arduino.cc/)
+//
+// This software is released under the GNU General Public License version 3,
+// which covers the main part of arduino-cli.
+// The terms of this license can be found at:
+// https://www.gnu.org/licenses/gpl-3.0.en.html
+//
+// You can be released from the requirements of the above licenses by purchasing
+// a commercial license. Buying such a license is mandatory if you want to
+// modify or otherwise use the software for commercial activities involving the
+// Arduino software without disclosing the source code of your own applications.
+// To purchase a commercial license, send an email to license@arduino.cc.
+
+package preprocessor
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	"github.com/arduino/arduino-cli/internal/arduino/sketch"
+	"github.com/arduino/go-paths-helper"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCtagsSketchFilter(t *testing.T) {
+	sourcePath := paths.New("testdata", "sketch_merged.cpp")
+	f, err := sourcePath.Open()
+	require.NoError(t, err)
+	t.Cleanup(func() { f.Close() })
+
+	sketch := &sketch.Sketch{
+		MainFile: paths.New("/home/megabug/Arduino/Test/Test.ino"),
+	}
+	stderr := bytes.NewBuffer(nil)
+	res := filterSketchSource(sketch, f, false, stderr)
+	require.Empty(t, stderr)
+	require.NotEmpty(t, res)
+	fmt.Println(res)
+}