lib.TarIo: Add unit tests

TarIo._match() and _filter_tar_file() are pure logic without test coverage.

Add unit tests for the exact path matching, the unfiltered round trip,
filtered extraction with a matched list, and a filter without hits.

Signed-off-by: Jan Lindemann <jan@janware.com>
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.85.1

test/unit/python/jw/pkg/lib/TarIo/Makefile

@@ -0,0 +1,7 @@
+TOPDIR = ../../../../../../..
+
+include $(TOPDIR)/make/proj.mk
+include $(JWBDIR)/make/py-run.mk
+
+all:
+test: run

test/unit/python/jw/pkg/lib/TarIo/test.py

@@ -0,0 +1,53 @@
+import io
+import tarfile
+
+from jw.pkg.lib.TarIo import TarIoTarFile
+
+def make_tar(files: dict[str, bytes]) -> bytes:
+    buf = io.BytesIO()
+    with tarfile.open(fileobj = buf, mode = 'w') as tf:
+        for name, content in files.items():
+            info = tarfile.TarInfo(name)
+            info.size = len(content)
+            tf.addfile(info, io.BytesIO(content))
+    return buf.getvalue()
+
+def members(blob: bytes) -> dict[str, bytes | None]:
+    ret = {}
+    with tarfile.open(fileobj = io.BytesIO(blob)) as tf:
+        for info in tf.getmembers():
+            f = tf.extractfile(info)
+            ret[info.name] = f.read() if f is not None else None
+    return ret
+
+# -- Bypass the constructor: _filter_tar_file() and _match() do not use
+# the copy contexts, so a bare instance is sufficient
+tar = object.__new__(TarIoTarFile)
+
+files = {
+    'a.txt': b'AAA',
+    'dir/b.txt': b'BBB',
+    'c.txt': b'CCC',
+}
+blob = make_tar(files)
+
+# -- _match is exact matching
+assert tar._match('a.txt', ['a.txt', 'c.txt'])
+assert not tar._match('a.txt', ['x.txt'])
+assert not tar._match('a.txt', [])
+
+# -- _filter_tar_file without a filter is a round trip
+ret = tar._filter_tar_file(blob)
+assert members(ret) == files
+
+# -- With a filter, only the exact paths survive
+matched: list[str] = []
+ret = tar._filter_tar_file(blob, ['a.txt', 'c.txt'], matched = matched)
+assert members(ret) == {'a.txt': b'AAA', 'c.txt': b'CCC'}
+assert sorted(matched) == ['a.txt', 'c.txt']
+
+# -- A filter without hits yields an empty tar
+ret = tar._filter_tar_file(blob, ['nope.txt'])
+assert members(ret) == {}
+
+print('All TarIo tests passed')