Add tests for axis letter

test/axis_letter.jl

@@ -0,0 +1,24 @@
+
+@testset "axis letter" begin
+    using Plots, RecipesBase
+    # a custom type for dispacthing the axis-letter-testing recipe
+    struct MyType <: Number
+        val::Float64
+    end
+    value(m::MyType) = m.val
+    data = MyType.(sort(randn(20)))
+    # A recipe that puts the axis letter in the title
+    @recipe function f(::Type{T}, m::T) where T <: AbstractArray{<:MyType}
+        title --> string(plotattributes[:letter])
+        value.(m)
+    end
+    @testset "$f (orientation = $o)" for f in [histogram, barhist, stephist, scatterhist], o in [:vertical, :horizontal]
+        @test f(data, orientation=o).subplots[1].attr[:title] == (o == :vertical ? "x" : "y")
+    end
+    @testset "$f" for f in [hline, hspan]
+        @test f(data).subplots[1].attr[:title] == "y"
+    end
+    @testset "$f" for f in [vline, vspan]
+        @test f(data).subplots[1].attr[:title] == "x"
+    end
+end

test/runtests.jl

@@ -9,8 +9,10 @@ using Gtk
 using LibGit2
 import GeometryTypes, GeometryBasics
 using Dates
+using RecipesBase
 
 include("test_axes.jl")
+include("axis_letter.jl")
 include("test_recipes.jl")
 include("test_hdf5plots.jl")
 include("test_pgfplotsx.jl")