Add tests for PlotlyJS backend

Project.toml

@@ -63,6 +63,7 @@ Images = "916415d5-f1e6-5110-898d-aaa5f9f070e0"
 LibGit2 = "76f85450-5226-5b5a-8eaa-529ad045b433"
 OffsetArrays = "6fe1bfb0-de20-5000-8ca7-80f57d26f881"
 PGFPlotsX = "8314cec4-20b6-5062-9cdb-752b83310925"
+PlotlyJS = "f0f68f2c-4968-5e81-91da-67840de0976a"
 RDatasets = "ce6b1742-4840-55fa-b093-852dadbb1d8b"
 StableRNGs = "860ef19b-820b-49d6-a774-d7a799459cd3"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
@@ -73,4 +74,4 @@ UnicodePlots = "b8865327-cd53-5732-bb35-84acbb429228"
 VisualRegressionTests = "34922c18-7c2a-561c-bac1-01e79b2c4c92"
 
 [targets]
-test = ["Distributions", "FileIO", "Gtk", "ImageMagick", "Images", "LibGit2", "OffsetArrays", "PGFPlotsX", "HDF5", "RDatasets", "StableRNGs", "StaticArrays", "StatsPlots", "Test", "TestImages", "UnicodePlots", "VisualRegressionTests"]
+test = ["Distributions", "FileIO", "Gtk", "ImageMagick", "Images", "LibGit2", "OffsetArrays", "PGFPlotsX", "PlotlyJS", "HDF5", "RDatasets", "StableRNGs", "StaticArrays", "StatsPlots", "Test", "TestImages", "UnicodePlots", "VisualRegressionTests"]

test/runtests.jl

@@ -139,6 +139,15 @@ const IMG_TOL = VERSION < v"1.4" && Sys.iswindows() ? 1e-1 : is_ci() ? 1e-2 : 1e
         @test isa(display(p), Nothing) == true
     end
 
+    @testset "PlotlyJS" begin
+        @test plotlyjs() == Plots.PlotlyJSBackend()
+        @test backend() == Plots.PlotlyJSBackend()
+
+        p = plot(rand(10))
+        @test isa(p, Plots.Plot) == true
+        @test_broken isa(display(p), Nothing) == true
+    end
+
 end
 
 @testset "Axes" begin
@@ -156,6 +165,10 @@ end
 end
 
 @testset "NoFail" begin
+    #ensure backend with tested display
+    @test unicodeplots() == Plots.UnicodePlotsBackend()
+    @test backend() == Plots.UnicodePlotsBackend()
+
     plots = [histogram([1, 0, 0, 0, 0, 0]),
              plot([missing]),
              plot([missing; 1:4]),