Refactor test/Containers into functional form (#3158)

Author: odow

test/Containers/Containers.jl

@@ -11,9 +11,8 @@
 using Test
 
 @testset "Containers" begin
-    @testset "$(file)" for file in
-                           filter(f -> endswith(f, ".jl"), readdir(@__DIR__))
-        if file in ["Containers.jl"]
+    @testset "$(file)" for file in readdir(@__DIR__)
+        if !endswith(file, ".jl") || file in ["Containers.jl"]
             continue
         end
         include(joinpath(@__DIR__, file))