Expand type of a property with union and add tests on it

src/Mesh/Mesh.jl

@@ -159,10 +159,21 @@ julia> add_property!(r, :absorbed_PAR, [0.0, 0.0]);
 function add_property!(m::Mesh, prop::Symbol, data, nt = ntriangles(m))
     # Check if the data is an array and if not convert it to an array with length nt
     vecdata = data isa AbstractVector ? data : fill(data, nt)
+    # Create new property if the one being added does not exist
     if !haskey(properties(m), prop)
         properties(m)[prop] = vecdata
+    # Otherwise append the data to the existing property creating an union type if necessary
+    # when the type of `data` does not inherit from the type of the existing property
     else
-        append!(properties(m)[prop], vecdata)
+        etype1 = eltype(properties(m)[prop])
+        etype2 = eltype(vecdata)
+        if etype2 isa etype1
+            append!(properties(m)[prop], vecdata)
+        else
+            etype3 = Union{etype1, etype2}
+            properties(m)[prop] = convert(Vector{etype3}, properties(m)[prop])
+            append!(properties(m)[prop], vecdata)
+        end
     end
     return m
 end

test/runtests.jl

@@ -71,3 +71,8 @@ end
 @testset "mesh_io" begin
     include("test_meshio.jl")
 end
+
+# Different cases where properties are added
+@testset "properties" begin
+    include("test_properties.jl")
+end

test/test_properties.jl

@@ -0,0 +1,28 @@
+import PlantGeomPrimitives as PGP
+using Test
+
+
+module dummy
+    struct bar end
+
+    struct foo end
+
+    struct oomp end
+end
+
+let
+
+import .dummy as D
+
+r = PGP.Rectangle()
+e = PGP.Ellipse()
+t = PGP.Triangle()
+
+PGP.add_property!(r, :prop, D.bar())
+eltype(PGP.properties(r)[:prop]) == D.bar
+PGP.add!(r, e, prop = D.foo())
+eltype(PGP.properties(r)[:prop]) == Union{D.bar, D.foo}
+PGP.add!(r, t, prop = D.oomp())
+eltype(PGP.properties(r)[:prop]) == Union{D.bar, D.foo, D.oomp}
+
+end