lib.ProcFilter: Add unit tests

ProcPipeline and the run() helper are pure logic without test coverage.

Add unit tests for the identity filter, chained filter execution order, the
append() layouts, and the chain handling of run().

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/ProcFilter/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/ProcFilter/test.py

@@ -0,0 +1,64 @@
+import asyncio
+
+from typing import override
+
+from jw.pkg.lib.ProcFilter import ProcFilter, ProcFilterIdentity, ProcPipeline, run
+from jw.pkg.lib.Result import Result
+
+class Upper(ProcFilter):
+
+    @override
+    async def _run(self, data: bytes | None) -> Result:
+        return Result(data.upper() if data else None, None, 0)
+
+class Exclaim(ProcFilter):
+
+    @override
+    async def _run(self, data: bytes | None) -> Result:
+        return Result(data + b'!' if data else None, None, 0)
+
+# -- ProcFilterIdentity --
+
+assert asyncio.run(ProcFilterIdentity().run(b'abc')).stdout == b'abc'
+# A None input comes back as a result with no output; stdout would
+# report b'' for a status-0 result, so use stdout_or_none here
+assert asyncio.run(ProcFilterIdentity().run(None)).stdout_or_none is None
+assert asyncio.run(ProcFilterIdentity().run(b'abc')).status == 0
+
+# -- ProcPipeline --
+
+# A single filter
+pl = ProcPipeline(Upper())
+assert asyncio.run(pl.run(b'abc')).stdout == b'ABC'
+
+# Filters are applied in order
+pl = ProcPipeline([Upper(), Exclaim()])
+assert asyncio.run(pl.run(b'abc')).stdout == b'ABC!'
+
+# append() accepts filters and iterables of filters, nested
+pl = ProcPipeline()
+pl.append(Upper())
+pl.append([Exclaim()])
+assert asyncio.run(pl.run(b'abc')).stdout == b'ABC!'
+
+# Input may be bytes or a Result
+assert asyncio.run(pl.run(Result(b'abc', None, 0))).stdout == b'ABC!'
+
+# An empty pipeline is the identity
+pl = ProcPipeline()
+assert asyncio.run(pl.run(b'abc')).stdout == b'abc'
+
+# -- run() --
+
+# Without a chain, bytes are wrapped and Results pass through
+ret = asyncio.run(run(b'abc'))
+assert isinstance(ret, Result) and ret.stdout == b'abc'
+r = Result(b'xyz', None, 0)
+assert asyncio.run(run(r)) is r
+
+# A single filter and a list of filters are both accepted
+assert asyncio.run(run(b'abc', Upper())).stdout == b'ABC'
+assert asyncio.run(run(b'abc', [Upper(), Exclaim()])).stdout == b'ABC!'
+assert asyncio.run(run(b'abc', ProcPipeline([Upper()]))).stdout == b'ABC'
+
+print('All ProcFilter tests passed')