Tests for .fc.

Including the various tricky cases.

S32-str/fc.t

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+use Test;
+
+plan 12;
+
+# Simple
+is 'BEEF \o/'.fc, 'beef \o/', '.fc on simple string in ASCII range works';
+is 'ÝØÛ SMĚŁŁ'.fc, 'ýøû směłł', '.fc on string with non-growing case fold';
+
+# Growing to multiple graphemes
+is 'Scheiße!'.fc, 'scheisse!', '.fc on ß expands to ss';
+is 'fish ʼn chips'.fc, 'fish ʼn chips', '.fc on ʼn expands to ʼn';
+is 'Leffe'.fc, 'leffe', 'ligature ff expands to ff on foldcase';
+is 'Efficient'.fc, 'efficient', 'ligature ffi expands to ffi on foldcase';
+
+# Curious cases where a foldcase does expand to a base and combiner, but NFC
+# (not even NFG) actually restores it, making it a no-op for NFG strings.
+is 'ǰnthn'.fc, 'ǰnthn', 'ǰ foldcases to identity under NFG (1 combiner)';
+is 'pΐvo'.fc, 'pΐvo', 'ΐ foldcases to identity under NFG (2 combiners)';
+
+# Cases where foldcase expands to precomposed and another base.
+is 'BᾈR'.fc, 'bἀιr', 'ᾈ foldcases to ἀι';
+is 'BᾈR'.fc.chars, 4, 'ᾈ -> ἀι = 1 extra char';
+
+# Case where foldcase expands to base, combiner, base, and we need to compose
+# the first two to maintain NFG.
+is 'oῷ!'.fc, 'oῶι!', 'ῷ foldcases to ῶι';
+is 'oῷ!'.fc.chars, 4, 'ῷ -> ῶι = 1 extra char';