Explicitly test eachregion

While this is implicitly tested later on, I think it's nice to test for
it explicitly. If nothing else, should any potentially buggy
modifications be made in the future it will make it easier to pin down
the root misbehaviour.

test/runtests.jl

@@ -3,7 +3,7 @@
 using Test
 
 using StyledStrings: StyledStrings, Legacy, SimpleColor, FACES, Face,
-    @styled_str, styled, StyledMarkup, getface, addface!, loadface!, resetfaces!
+    @styled_str, styled, StyledMarkup, eachregion, getface, addface!, loadface!, resetfaces!
 using .StyledMarkup: MalformedStylingMacro
 using Base: AnnotatedString, AnnotatedChar, AnnotatedIOBuffer, annotations
 
@@ -35,6 +35,50 @@ end
 # When tested as part of the stdlib, the package prefix can start appearing in show methods.
 choppkg(s::String) = chopprefix(s, "StyledStrings.")
 
+@testset "Eachregion" begin
+    annregions(str::String, annots::Vector{<:Tuple{UnitRange{Int}, <:Pair{Symbol, <:Any}}}) =
+        collect(eachregion(AnnotatedString(str, annots)))
+    # Regions that do/don't extend to the left/right edges
+    @test annregions(" abc ", [(2:4, :face => :bold)]) ==
+        [(" ", []),
+         ("abc", [:face => :bold]),
+         (" ", [])]
+    @test annregions(" x ", [(2:2, :face => :bold)]) ==
+        [(" ", []),
+         ("x", [:face => :bold]),
+         (" ", [])]
+    @test annregions(" x", [(2:2, :face => :bold)]) ==
+        [(" ", []),
+         ("x", [:face => :bold])]
+    @test annregions("x ", [(1:1, :face => :bold)]) ==
+        [("x", [:face => :bold]),
+         (" ", [])]
+    @test annregions("x", [(1:1, :face => :bold)]) ==
+        [("x", [:face => :bold])]
+    # Overlapping/nested regions
+    @test annregions(" abc ", [(2:4, :face => :bold), (3:3, :face => :italic)]) ==
+        [(" ", []),
+         ("a", [:face => :bold]),
+         ("b", [:face => :bold, :face => :italic]),
+         ("c", [:face => :bold]),
+         (" ", [])]
+    @test annregions("abc-xyz", [(1:7, :face => :bold), (1:3, :face => :green), (4:4, :face => :yellow), (4:7, :face => :italic)]) ==
+        [("abc", [:face => :bold, :face => :green]),
+         ("-", [:face => :bold, :face => :yellow, :face => :italic]),
+         ("xyz", [:face => :bold, :face => :italic])]
+    # Preserving annotation order
+    @test annregions("abcd", [(1:3, :face => :red), (2:2, :face => :yellow), (2:3, :face => :green), (2:4, :face => :blue)]) ==
+        [("a", [:face => :red]),
+         ("b", [:face => :red, :face => :yellow, :face => :green, :face => :blue]),
+         ("c", [:face => :red, :face => :green, :face => :blue]),
+         ("d", [:face => :blue])]
+    @test annregions("abcd", [(2:4, :face => :blue), (1:3, :face => :red), (2:3, :face => :green), (2:2, :face => :yellow)]) ==
+        [("a", [:face => :red]),
+         ("b", [:face => :blue, :face => :red, :face => :green, :face => :yellow]),
+         ("c", [:face => :blue, :face => :red, :face => :green]),
+         ("d", [:face => :blue])]
+end
+
 @testset "SimpleColor" begin
     @test SimpleColor(:hey).value == :hey # no error
     @test SimpleColor(0x01, 0x02, 0x03).value == (r=0x01, g=0x02, b=0x03)