1 files changed, 30 insertions, 0 deletions

diff --git a/internal/norm/norm_test.go b/internal/norm/norm_test.go
index 885c6f7..a165b32 100644
--- a/internal/norm/norm_test.go
+++ b/internal/norm/norm_test.go
@@ -73,3 +73,33 @@ func TestFoldASCIINoAlloc(t *testing.T) {
 		t.Errorf("Fold allocates %v times on ASCII input", n)
 	}
 }
+
+// TestFoldMappedSource: a part of the folded text leads back to the original
+// characters it came from, widened to whole characters - so a capture can be
+// written with its diacritics.
+func TestFoldMappedSource(t *testing.T) {
+	cases := []struct {
+		in, folded string
+		a, b       int
+		want       string
+	}{
+		{"Łódź-faktura.pdf", "Lodz-faktura.pdf", 0, 4, "Łódź"},
+		{"Łódź-faktura.pdf", "Lodz-faktura.pdf", 5, 12, "faktura"},
+		{"straße", "strasse", 4, 5, "ß"},
+		{"áb", "ab", 0, 1, "a"},
+		{"áb", "ab", 1, 2, "b"},
+		{"\xff\xfeé", "�e", 0, 3, "\xff\xfe"},
+		{"plain.txt", "plain.txt", 0, 5, "plain"},
+		{"Łódź", "Lodz", 2, 2, ""},
+	}
+	for _, c := range cases {
+		f := FoldMapped(c.in)
+		if f.Text != c.folded || f.Text != Fold(c.in) {
+			t.Errorf("FoldMapped(%q).Text = %q, want %q (Fold)", c.in, f.Text, c.folded)
+			continue
+		}
+		if got := f.Source(c.a, c.b); got != c.want {
+			t.Errorf("FoldMapped(%q).Source(%d, %d) = %q, want %q", c.in, c.a, c.b, got, c.want)
+		}
+	}
+}