added tests for begin indexing

Author: torfjelde

test/dynamiclens_begin.jl

@@ -0,0 +1,18 @@
+l = @lens _[begin]
+@test l isa Setfield.DynamicIndexLens
+obj = (1,2,3)
+@test get(obj, l) == 1
+@test set(obj, l, true) == (true,2,3)
+
+l = @lens _[2*begin]
+@test l isa Setfield.DynamicIndexLens
+obj = (1,2,3)
+@test get(obj, l) == 2
+@test set(obj, l, true) == (1,true,3)
+
+one = 1
+plustwo(x) = x + 2
+l = @lens _.a[plustwo(begin) - one].b
+obj = (a=(1, (a=10, b=20), 3), b=4)
+@test get(obj, l) == 20
+@test set(obj, l, true) == (a=(1, (a=10, b=true), 3), b=4)

test/test_core.jl

@@ -281,6 +281,12 @@ end
     obj = (a=(1, (a=10, b=20), 3), b=4)
     @test get(obj, l) == 20
     @test set(obj, l, true) == (a=(1, (a=10, b=true), 3), b=4)
+
+    if Setfield.HAS_BEGIN_INDEXING
+        # Need to keep this in a separate file since `begin` won't parse
+        # on older Julia versions.
+        include("dynamiclens_begin.jl")
+    end
 end
 
 @testset "StaticNumbers" begin