[education/labplot] tests/cartesianplot: Added a unit test for the single instance of Legen in CartesianPlot.

Git commit e8e7a414eb0bc7fbd876cbe981af27cd3f30ab6d by Alexander Semke.
Committed on 10/08/2026 at 20:13.
Pushed by asemke into branch 'master'.

Added a unit test for the single instance of Legen in CartesianPlot.

M  +20   -0    tests/cartesianplot/CartesianPlotTest.cpp
M  +3    -0    tests/cartesianplot/CartesianPlotTest.h

https://invent.kde.org/education/labplot/-/commit/e8e7a414eb0bc7fbd876cbe981af27cd3f30ab6d

diff --git a/tests/cartesianplot/CartesianPlotTest.cpp b/tests/cartesianplot/CartesianPlotTest.cpp
index 8540d0af11..6284651db3 100644
--- a/tests/cartesianplot/CartesianPlotTest.cpp
+++ b/tests/cartesianplot/CartesianPlotTest.cpp
@@ -21,6 +21,7 @@
 #include "backend/worksheet/InfoElement.h"
 #include "backend/worksheet/plots/cartesian/CartesianCoordinateSystem.h"
 #include "backend/worksheet/plots/cartesian/CartesianPlot.h"
+#include "backend/worksheet/plots/cartesian/CartesianPlotLegend.h"
 #include "backend/worksheet/plots/cartesian/CartesianPlotPrivate.h"
 #include "backend/worksheet/plots/cartesian/plots.h"
 #include "frontend/dockwidgets/XYFitCurveDock.h"
@@ -1796,4 +1797,23 @@ void CartesianPlotTest::zValueAfterAddMoveRemove() {
 	QVERIFY(zValueCurve1 < zValueHistogram);
 }
 
+void CartesianPlotTest::legendSingleInstance() {
+	auto* project = new Project();
+	auto* worksheet = new Worksheet(QStringLiteral("ws"));
+	project->addChild(worksheet);
+
+	auto* plot = new CartesianPlot(QStringLiteral("plot"));
+	worksheet->addChild(plot);
+
+	// first call creates the legend
+	plot->addLegend();
+	QCOMPARE(plot->childCount<CartesianPlotLegend>(), 1);
+
+	// second call must be a no-op — only one legend is allowed
+	plot->addLegend();
+	QCOMPARE(plot->childCount<CartesianPlotLegend>(), 1);
+
+	delete project;
+}
+
 QTEST_MAIN(CartesianPlotTest)
diff --git a/tests/cartesianplot/CartesianPlotTest.h b/tests/cartesianplot/CartesianPlotTest.h
index 3d35ab6f2d..6a60c9baeb 100644
--- a/tests/cartesianplot/CartesianPlotTest.h
+++ b/tests/cartesianplot/CartesianPlotTest.h
@@ -71,5 +71,8 @@ private Q_SLOTS:
 
 	// handling of z-values on changes in the child hierarchy
 	void zValueAfterAddMoveRemove();
+
+	// legend
+	void legendSingleInstance();
 };
 #endif