Fix knobs not updating vals on link (#4904)

tests/CMakeLists.txt

@@ -18,6 +18,7 @@ ADD_EXECUTABLE(tests
 	QTestSuite
 	$<TARGET_OBJECTS:lmmsobjs>
 
+	src/core/AutomatableModelTest.cpp
 	src/core/ProjectVersionTest.cpp
 	src/core/RelativePathsTest.cpp
 

tests/src/core/AutomatableModelTest.cpp

@@ -0,0 +1,67 @@
+/*
+ * AutomatableModelTest.cpp
+ *
+ * Copyright (c) 2020 Johannes Lorenz <j.git$$$lorenz-ho.me, $$$=@>
+ *
+ * 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 "AutomatableModel.h"
+
+class AutomatableModelTest : QTestSuite
+{
+	Q_OBJECT
+
+	bool m1Changed, m2Changed;
+	void resetChanged() { m1Changed = m2Changed = false; }
+
+private slots: // helper slots
+	void onM1Changed(Model* ) { m1Changed = true; }
+	void onM2Changed(Model* ) { m2Changed = true; }
+
+private slots: // tests
+	void LinkTests()
+	{
+		BoolModel m1(false), m2(false);
+
+		QObject::connect(&m1, SIGNAL(dataChanged(Model*)),
+			this, SLOT(onM1Changed(Model*)));
+		QObject::connect(&m2, SIGNAL(dataChanged(Model*)),
+			this, SLOT(onM2Changed(Model*)));
+
+		resetChanged();
+		AutomatableModel::linkModels(&m1, &m1);
+		QVERIFY(!m1Changed); // cannot link to itself
+		QVERIFY(!m2Changed);
+
+		resetChanged();
+		AutomatableModel::linkModels(&m1, &m2);
+		QVERIFY(m1Changed); // since m1 takes the value of m2
+		QVERIFY(!m2Changed); // the second model is the source
+
+		resetChanged();
+		AutomatableModel::linkModels(&m1, &m2);
+		QVERIFY(!m1Changed); // it's already linked
+		QVERIFY(!m2Changed);
+	}
+} AutomatableModelTests;
+
+#include "AutomatableModelTest.moc"