add tests

test/runtests.jl

@@ -11,6 +11,19 @@ import GeometryTypes, GeometryBasics
 using Dates
 using RecipesBase
 
+# NOTE: you can run this test only once
+@testset "Plotly standalone" begin
+    @test_throws UndefRefError Plots.plotly_local_file_path[]
+    temp = Plots.use_local_dependencies[]
+    withenv("PLOTS_HOST_DEPENDENCY_LOCAL" => true) do
+        Plots.__init__()
+        @test Plots.plotly_local_file_path[] isa String
+        @test isfile(Plots.plotly_local_file_path[])
+        @test Plots.use_local_dependencies[] = true
+    end
+    Plots.use_local_dependencies[] = temp
+end # testset
+
 include("test_defaults.jl")
 include("test_axes.jl")
 include("test_axis_letter.jl")