Update test_defaults.jl

Fix #3053 

Needs test

src/init.jl

@@ -15,9 +15,10 @@ end
 function __init__()
     user_defaults = _plots_defaults()
     if haskey(user_defaults, :theme)
-        theme(pop!(user_defaults, :theme))
+        theme(pop!(user_defaults, :theme); user_defaults...)
+    else
+        default(; user_defaults...)
     end
-    default(; user_defaults...)
 
     insert!(Base.Multimedia.displays, findlast(x -> x isa Base.TextDisplay || x isa REPL.REPLDisplay, Base.Multimedia.displays) + 1, PlotsDisplay())
 

test/runtests.jl

@@ -11,6 +11,7 @@ import GeometryTypes, GeometryBasics
 using Dates
 using RecipesBase
 
+include("test_defaults.jl")
 include("test_axes.jl")
 include("test_axis_letter.jl")
 include("test_recipes.jl")

test/test_defaults.jl

@@ -0,0 +1,11 @@
+using Plots, Test
+
+const PLOTS_DEFAULTS = Dict(:theme => :wong2)
+Plots.__init__()
+
+@testset "Loading theme" begin
+    @test plot(1:5)[1][1][:seriescolor] == RGBA(colorant"black")
+end
+
+empty!(PLOTS_DEFAULTS)
+Plots.__init__()