1 files changed, 30 insertions, 0 deletions
diff --git a/internal/norm/fuzz_test.go b/internal/norm/fuzz_test.go
new file mode 100644
index 0000000..fde62a0
--- /dev/null
+++ b/internal/norm/fuzz_test.go
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package norm
+
+import "testing"
+
+// FuzzTextIdempotent: normalising text twice changes nothing more than
+// normalising it once, under every case and fold setting, and so for names.
+// Keywords are normalised at load and text at match time by the same
+// functions; a second pass that still changed something would mean the two
+// could disagree about what one normalised string is.
+func FuzzTextIdempotent(f *testing.F) {
+	for _, s := range []string{"Spółka Z O.O.", "ẞ straße", "a\u0301", "  tabs\tand\nlines ", "\xff", "İstanbul", "ǅ", "Æsir Œuvre"} {
+		f.Add(s)
+	}
+	f.Fuzz(func(t *testing.T, s string) {
+		for _, opt := range [][2]bool{{false, false}, {true, false}, {false, true}, {true, true}} {
+			once := Text(s, opt[0], opt[1])
+			if twice := Text(once, opt[0], opt[1]); twice != once {
+				t.Fatalf("Text(%q, %v, %v) = %q, again %q", s, opt[0], opt[1], once, twice)
+			}
+		}
+		for _, fold := range []bool{false, true} {
+			once := Name(s, fold)
+			if twice := Name(once, fold); twice != once {
+				t.Fatalf("Name(%q, %v) = %q, again %q", s, fold, once, twice)
+			}
+		}
+	})
+}