[test][spline] Set gnuplot.setOpenPlotWindow(false) to avoid gnuplot timeout

test/common/spline/test_cubicspline.cc

@@ -85,6 +85,7 @@ int main(int argc, char** argv)
     const auto resultDerivPlot = eval([&](const double x) { return spline.evalDerivative(x); }, plotPoints);
 
     Dumux::GnuplotInterface<double> gnuplot(false);
+    gnuplot.setOpenPlotWindow(false);
     gnuplot.addDataSetToPlot(plotPoints, refPlot, "reference");
     gnuplot.addDataSetToPlot(plotPoints, refDerivPlot, "reference_derivative");
     gnuplot.addDataSetToPlot(plotPoints, resultPlot, "spline");

test/common/spline/test_monotonecubicspline.cc

@@ -115,6 +115,7 @@ int main(int argc, char** argv)
     const auto resultDerivPlot = eval([&](const double x) { return spline.evalDerivative(x); }, plotPoints);
 
     Dumux::GnuplotInterface<double> gnuplot(/*persist=*/false);
+    gnuplot.setOpenPlotWindow(false);
     gnuplot.addDataSetToPlot(plotPoints, refPlot, "exp_reference");
     gnuplot.addDataSetToPlot(plotPoints, refDerivPlot, "exp_reference_derivative");
     gnuplot.addDataSetToPlot(plotPoints, resultPlot, "monotspline");