1 files changed, 46 insertions, 0 deletions

diff --git a/src/pkg/unicode/letter_test.go b/src/pkg/unicode/letter_test.go
index 4c24ffc51..c4e26df58 100644
--- a/src/pkg/unicode/letter_test.go
+++ b/src/pkg/unicode/letter_test.go
@@ -376,3 +376,49 @@ func TestTurkishCase(t *testing.T) {
 		}
 	}
 }
+
+var simpleFoldTests = []string{
+	// SimpleFold could order its returned slices in any order it wants,
+	// but we know it orders them in increasing order starting at in
+	// and looping around from MaxRune to 0.
+
+	// Easy cases.
+	"Aa",
+	"aA",
+	"δΔ",
+	"Δδ",
+
+	// ASCII special cases.
+	"KkK",
+	"kKK",
+	"KKk",
+	"Ssſ",
+	"sſS",
+	"ſSs",
+
+	// Non-ASCII special cases.
+	"ρϱΡ",
+	"ϱΡρ",
+	"Ρρϱ",
+	"ͅΙιι",
+	"Ιιιͅ",
+	"ιιͅΙ",
+	"ιͅΙι",
+
+	// Extra special cases: has lower/upper but no case fold.
+	"İ",
+	"ı",
+}
+
+func TestSimpleFold(t *testing.T) {
+	for _, tt := range simpleFoldTests {
+		cycle := []int(tt)
+		rune := cycle[len(cycle)-1]
+		for _, out := range cycle {
+			if r := SimpleFold(rune); r != out {
+				t.Errorf("SimpleFold(%#U) = %#U, want %#U", rune, r, out)
+			}
+			rune = out
+		}
+	}
+}