Activate TestEnv if needed

Author: ufechner7

examples/menu.jl

@@ -1,3 +1,8 @@
+using Pkg
+if ! ("ControlPlots" ∈ keys(Pkg.project().dependencies))
+    using TestEnv; TestEnv.activate()
+end
+
 using ControlPlots
 using VortexStepMethod
 using REPL.TerminalMenus