diff --git a/test/unit/python/jw/pkg/lib/ProcFilter/Makefile b/test/unit/python/jw/pkg/lib/ProcFilter/Makefile
new file mode 100644
index 00000000..de693650
--- /dev/null
+++ b/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
diff --git a/test/unit/python/jw/pkg/lib/ProcFilter/test.py b/test/unit/python/jw/pkg/lib/ProcFilter/test.py
new file mode 100644
index 00000000..250c9b8f
--- /dev/null
+++ b/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')