Display labels at the bottom and as a column in a ParametricPlot3D

Question

I would like to display the labels of a 3D plot (made of many subplots) as a column at the bottom of the plot. I managed to put them at the bottom, thanks to the option Placed, but they are always displayed in a row. How can I put them in column?

Here is a minimal working example. The actual code is much more lengthy.

test1 = Quiet@ParametricPlot3D[{u, 0, 0}, {u, 0, 1}, PlotLegends -> Placed[{"test1"}, Bottom]];
test2 = Quiet@ParametricPlot3D[{0, u, 0}, {u, 0, 1}, PlotLegends -> Placed[{"test2"}, Bottom]];
test3 = Quiet@ParametricPlot3D[{0, 0, u}, {u, 0, 1}, PlotLegends -> Placed[{"test3"}, Bottom]];
Show[test1, test2, test3]

The overall structure is fixed (I cannot plot test1, test2 and test3 as a single plot but I have to merge them through Show).

Thank you.

Answer 1

You can extract the graphics and the legends from the output of Show and reorganize the legends as follows:

test1 =   ParametricPlot3D[{u, 0, 0}, {u, 0, 1}, PlotStyle -> Red, 
       PlotLegends -> Placed[{"test1"}, Bottom]];
test2 =   ParametricPlot3D[{0, u, 0}, {u, 0, 1}, PlotStyle -> Blue, 
       PlotLegends -> Placed[{"test2"}, Bottom]];
test3 =  ParametricPlot3D[{0, 0, u}, {u, 0, 1}, PlotStyle -> Green, 
       PlotLegends -> Placed[{"test3"}, Bottom]];
show = Show[test1, test2, test3];
graphics = show[[1, 1, 1]];
legend = Column[SortBy[Cases[show, Placed[a_, __] :> a, {0, Infinity}], #[[2, 1]] &]];

Legended[graphics, Placed[legend, Bottom]] (* or *)
Labeled[graphics, legend]

Answer 2

Something like this?

Legended[
  Show[
    Plot3D[Sin[ x] + Cos[ y], {x, 0, 2 π}, {y, 0, 2 π}, PlotStyle -> Red],
    Plot3D[Sin[ x] - Cos[ y], {x, 0, 2 π}, {y, 0, 2 π}, PlotStyle -> Blue]],
 Placed[LineLegend[{Red, Blue}, {"test1", "test2"}], Below]]