Use sandboxing for examples

Author: blegat

examples/run_examples.jl

@@ -1,5 +1,18 @@
 using Test
 
+"""
+    _include_sandbox(filename)
+
+Include the `filename` in a temporary module that acts as a sandbox. (Ensuring
+no constants or functions leak into other files.)
+
+This function was taken from `JuMP/docs/make.jl`.
+"""
+function _include_sandbox(filename)
+    mod = @eval module $(gensym()) end
+    return Base.include(mod, filename)
+end
+
 const _TUTORIAL_DIR = joinpath(@__DIR__, "..", "docs", "src", "tutorials")
 
 @testset "run_examples.jl" begin
@@ -9,7 +22,7 @@ const _TUTORIAL_DIR = joinpath(@__DIR__, "..", "docs", "src", "tutorials")
                 continue
             end
             path = joinpath(_TUTORIAL_DIR, dir, filename)
-            include(path)
+            _include_sandbox(path)
         end
     end
     @testset "Chordal" begin