rename test file and add to runtests.jl

Author: anandijain

test/tree_print.jl renamed to test/print_tree.jl

@@ -35,3 +35,4 @@ println("Last test requires gcc available in the path!")
 @safetestset "Latexify recipes Test" begin include("latexify.jl") end
 @safetestset "StructuralTransformations" begin include("structural_transformation/runtests.jl") end
 @testset "Serialization" begin include("serialization.jl") end
+@testset "print_tree" begin include("print_tree.jl") end