Lv2: Improve LED widget's digit calculation

This improves the way digits are calculated for display in
`Lv2ViewProc`:

- More than 2 digits are now recognized
- Minus signs are now recognized
- Tests have been added

tests/CMakeLists.txt

@@ -21,6 +21,7 @@ ADD_EXECUTABLE(tests
 
 	src/core/ArrayVectorTest.cpp
 	src/core/AutomatableModelTest.cpp
+	src/core/MathTest.cpp
 	src/core/ProjectVersionTest.cpp
 	src/core/RelativePathsTest.cpp
 

tests/src/core/MathTest.cpp

@@ -0,0 +1,53 @@
+/*
+ * MathTest.cpp
+ *
+ * Copyright (c) 2023 Johannes Lorenz <jlsf2013$users.sourceforge.net, $=@>
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include "QTestSuite.h"
+
+#include "lmms_math.h"
+
+#include <QDir>
+
+class MathTest : QTestSuite
+{
+	Q_OBJECT
+private slots:
+	void NumDigitsTest()
+	{
+		using namespace lmms;
+		QCOMPARE(numDigitsAsInt(1.f), 1);
+		QCOMPARE(numDigitsAsInt(9.9f), 2);
+		QCOMPARE(numDigitsAsInt(10.f), 2);
+		QCOMPARE(numDigitsAsInt(0.f), 1);
+		QCOMPARE(numDigitsAsInt(-100.f), 4);
+		QCOMPARE(numDigitsAsInt(-99.f), 3);
+		QCOMPARE(numDigitsAsInt(-0.4f), 1); // there is no "-0" for LED spinbox
+		QCOMPARE(numDigitsAsInt(-0.99f), 2);
+		QCOMPARE(numDigitsAsInt(1000000000), 10);
+		QCOMPARE(numDigitsAsInt(-1000000000), 11);
+		QCOMPARE(numDigitsAsInt(900000000), 9);
+		QCOMPARE(numDigitsAsInt(-900000000), 10);
+	}
+} MathTests;
+
+#include "MathTest.moc"