Test that next(s, endof(s)) > endof(s.data)

Author: TotalVerb

test/strings/basic.jl

@@ -427,3 +427,10 @@ foobaz(ch) = reinterpret(Char, typemax(UInt32))
 
 # issue #17624, missing getindex method for String
 @test "abc"[:] == "abc"
+
+# we assume for performance that next/nextind return values past the end of a
+# string's underlying data; this helps with performance of `done`.
+for s in ("Hello", "Σ", "こんにちは", "😊😁")
+    @test next(s, endof(s))[2] > endof(s.data)
+    @test nextind(s, endof(s)) > endof(s.data)
+end