Maint: split custom config files in openvpn/custom

internal/openvpn/custom/read_test.go

@@ -0,0 +1,32 @@
+package custom
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_readCustomConfigLines(t *testing.T) {
+	t.Parallel()
+
+	file, err := os.CreateTemp("", "")
+	require.NoError(t, err)
+	defer removeFile(t, file.Name())
+	defer file.Close()
+
+	_, err = file.WriteString("line one\nline two\nline three\n")
+	require.NoError(t, err)
+
+	err = file.Close()
+	require.NoError(t, err)
+
+	lines, err := readCustomConfigLines(file.Name())
+	assert.NoError(t, err)
+
+	expectedLines := []string{
+		"line one", "line two", "line three", "",
+	}
+	assert.Equal(t, expectedLines, lines)
+}