diff --git a/.github/workflows/run-tests-push.yml b/.github/workflows/run-tests-push.yml
index e71f440..75c4dcb 100644
--- a/.github/workflows/run-tests-push.yml
+++ b/.github/workflows/run-tests-push.yml
@@ -11,148 +11,60 @@ jobs:
     - uses: actions/setup-python@v5
       with:
         python-version: "3.9"
+        cache: 'pip'
     - run: sudo apt install xvfb
     - run: pip install --upgrade pip
     - run: pip install .[dev]
-    - run: xvfb-run pytest tests/
+    - run: xvfb-run pytest -v -rP --doctest-modules countess/ tests/
 
-  run-tests-ubuntu-22_04-python-3_10-with-coverage:
+  run-tests-ubuntu-22_04-python-3_10:
     runs-on: ubuntu-22.04
-    name: Ubuntu 22.04, Python 3.10 (with coverage)
+    name: Ubuntu 22.04, Python 3.10
     steps:
     - uses: actions/checkout@v4
     - uses: actions/setup-python@v5
       with:
         python-version: "3.10"
+        cache: 'pip'
     - run: sudo apt install xvfb
     - run: pip install --upgrade pip
     - run: pip install .[dev]
-    - run: xvfb-run coverage run --source countess -m pytest tests/
-#    - run: coverage html
-#    - uses: actions/upload-artifact@v3
-#      with:
-#        name: test coverage report
-#        path: htmlcov/*
-    - run: echo '### Coverage Report' >> $GITHUB_STEP_SUMMARY
-    - run: coverage report --format=markdown --skip-empty --sort=-cover >> $GITHUB_STEP_SUMMARY
-
-#  run-tests-ubuntu-22_04-python-3_11_0rc2:
-#   runs-on: ubuntu-22.04
-#    name: Ubuntu 22.04, Python 3.11.0rc2
-#    steps:
-#    - uses: actions/checkout@v4
-#    - uses: actions/setup-python@v4
-#      with:
-#        python-version: "3.11.0-rc.2"
-#    - run: sudo apt install xvfb
-#    - run: pip install --upgrade pip
-#    - run: pip install .[dev]
-#    - run: xvfb-run pytest tests/
-#
-#  run-tests-ubuntu-22_04-python-3_11_0:
-#    runs-on: ubuntu-22.04
-#    name: Ubuntu 22.04, Python 3.11.1
-#    steps:
-#    - uses: actions/checkout@v4
-#    - uses: actions/setup-python@v4
-#      with:
-#        python-version: "3.11.0"
-#    - run: sudo apt install xvfb
-#    - run: pip install --upgrade pip
-#    - run: pip install .[dev]
-#    - run: xvfb-run pytest tests/
-#
-#  run-tests-ubuntu-22_04-python-3_11_1:
-#    runs-on: ubuntu-22.04
-#    name: Ubuntu 22.04, Python 3.11.1
-#    steps:
-#    - uses: actions/checkout@v4
-#    - uses: actions/setup-python@v4
-#      with:
-#        python-version: "3.11.1"
-#    - run: sudo apt install xvfb
-#    - run: pip install --upgrade pip
-#    - run: pip install .[dev]
-#    - run: xvfb-run pytest tests/
-
-  run-tests-ubuntu-22_04-python-3_11_2:
-    runs-on: ubuntu-22.04
-    name: Ubuntu 22.04, Python 3.11.2
-    steps:
-    - uses: actions/checkout@v4
-    - uses: actions/setup-python@v5
-      with:
-        python-version: "3.11.2"
-    - run: sudo apt install xvfb
-    - run: pip install --upgrade pip
-    - run: pip install .[dev]
-    - run: xvfb-run pytest tests/
-
-  run-tests-ubuntu-22_04-python-3_11:
-    runs-on: ubuntu-22.04
-    name: Ubuntu 22.04, Python 3.11
-    steps:
-    - uses: actions/checkout@v4
-    - uses: actions/setup-python@v5
-      with:
-        python-version: "3.11"
-    - run: sudo apt install xvfb
-    - run: pip install --upgrade pip
-    - run: pip install .[dev]
-    - run: xvfb-run pytest tests/
-
-#  run-tests-ubuntu-22_04-python-3_12_0_alpha5:
-#    runs-on: ubuntu-22.04
-#    name: Ubuntu 22.04, Python 3.12.0alpha5
-#    steps:
-#    - uses: actions/checkout@v4
-#    - uses: actions/setup-python@v4
-#      with:
-#        python-version: "3.12.0-alpha.5"
-#    - run: sudo apt install xvfb
-#    - run: pip install --upgrade pip
-#    - run: pip install .[dev]
-#    - run: xvfb-run pytest tests/
+    - run: xvfb-run pytest -v -rP --doctest-modules countess/ tests/
 
   run-tests-ubuntu-22_04-python-3_11_from_apt:
     runs-on: ubuntu-22.04
-    name: Ubuntu 22.04, Python from Apt
+    name: Ubuntu 22.04, Python 3.11 from Apt
     steps:
     - uses: actions/checkout@v4
     - run: sudo apt install python3.11-full python3-pip xvfb
     - run: python3.11 -m pip install --upgrade pip
     - run: python3.11 -m pip install -e .[dev]
-    - run: xvfb-run python3.11 -mpytest tests/
+    - run: xvfb-run python3.11 -m pytest -v -rP --doctest-modules countess/ tests/
 
-      #  run-tests-ubuntu-22_10-python-3_11_from_apt:
-      #runs-on: ubuntu-22.10
-      #name: Ubuntu 22.10, Python from Apt
-      #steps:
-      #- uses: actions/checkout@v4
-      #- run: sudo apt install python3.11-full python3-pip xvfb
-      #- run: python3.11 -m pip install --upgrade pip
-      #- run: python3.11 -m pip install -e .[dev]
-      #- run: xvfb-run python3.11 -mpytest tests/
-
-      #run-tests-ubuntu-23_04-python-3_11_from_apt:
-      #runs-on: ubuntu-23.04
-      #name: Ubuntu 23.04, Python from Apt
-      #steps:
-      #- uses: actions/checkout@v4
-      #- run: sudo apt install python3.11-full python3-pip xvfb
-      #- run: python3.11 -m pip install --upgrade pip
-      #- run: python3.11 -m pip install -e .[dev]
-      #- run: xvfb-run python3.11 -mpytest tests/
+  run-tests-ubuntu-24_04-python-3_12_from_apt:
+    runs-on: ubuntu-24.04
+    name: Ubuntu 24.04, Python 3.12 from Apt
+    steps:
+    - uses: actions/checkout@v4
+    - run: sudo apt install python3.12-full python3-pip xvfb
+    - run: python3.12 -m venv /tmp/venv
+    - run: /tmp/venv/bin/python -m pip install --upgrade pip
+    - run: /tmp/venv/bin/python -m pip install -e .[dev]
+    - run: xvfb-run /tmp/venv/bin/python -m pytest -v -rP --doctest-modules countess/ tests/
 
-#  run-tests-ubuntu-22_04-pypy3:
-#    runs-on: ubuntu-22.04
-#    name: Ubuntu 22.04, PyPy 3
-#    steps:
-#    - uses: actions/checkout@v4
-#    - uses: actions/setup-python@v4
-#      with:
-#        python-version: "pypy3.9"
-#    - run: sudo apt install pypy3 pypy3-tk pypy3-dev xvfb
-#    - run: pypy3 -mpip install -U pip wheel
-#    - run: pypy3 -mpip install .[dev]
-#    - run: xvfb-run pytest tests/
+  run-tests-ubuntu-24_04-python-3_x:
+    runs-on: ubuntu-24.04
+    name: Ubuntu 24.04, Python 3.x
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-python@v5
+      with:
+        python-version: "3.x"
+        cache: 'pip'
+    - run: sudo apt install xvfb
+    - run: python3 -m venv /tmp/venv
+    - run: /tmp/venv/bin/python -m pip install --upgrade pip
+    - run: /tmp/venv/bin/python -m pip install -e .[dev]
+    - run: xvfb-run /tmp/venv/bin/coverage run --source countess -m pytest -v -rP --doctest-modules countess/ tests/
+    - run: echo '### Coverage Report' >> $GITHUB_STEP_SUMMARY
+    - run: /tmp/venv/bin/coverage report --format=markdown --skip-empty --sort=-cover >> $GITHUB_STEP_SUMMARY
diff --git a/countess/core/cmd.py b/countess/core/cmd.py
index a8d0364..b173060 100644
--- a/countess/core/cmd.py
+++ b/countess/core/cmd.py
@@ -17,15 +17,27 @@ def run(argv) -> None:
 
 
 def main() -> None:
+    # set up a default stderr StreamHandler for logs
+    logging_handler = logging.StreamHandler()
+
+    # set up a QueueHandler/QueueListener to forward the logs between
+    # processes and send them to the logging_handler
     logging_queue: multiprocessing.Queue = multiprocessing.Queue()
-    logging.getLogger().addHandler(logging.handlers.QueueHandler(logging_queue))
-    logging.getLogger().setLevel(logging.INFO)
-    logging_handler = logging.handlers.QueueListener(logging_queue, logging.StreamHandler())
-    logging_handler.start()
+    logging_queue_handler = logging.handlers.QueueHandler(logging_queue)
+    logging_queue_listener = logging.handlers.QueueListener(logging_queue, logging_handler)
+    logging_queue_listener.start()
+
+    # set up all loggers to be handled by the QueueHandler.
+    root_logger = logging.getLogger()
+    root_logger.addHandler(logging_queue_handler)
+    root_logger.setLevel(logging.INFO)
 
     run(sys.argv[1:])
 
-    logging_handler.stop()
+    # shut down the logging subsystem, in case this function is being
+    # called as part of something else (eg: tests)
+    root_logger.handlers.clear()
+    logging_queue_listener.stop()
     logging_queue.close()
 
 
diff --git a/countess/core/pipeline.py b/countess/core/pipeline.py
index 94f6475..4b983f7 100644
--- a/countess/core/pipeline.py
+++ b/countess/core/pipeline.py
@@ -18,8 +18,12 @@ class SentinelQueue(Queue):
     The writer is expected to call `queue.finish()` when it is done and
     the reader can treat the queue like an iterable."""
 
-    # XXX this is an attempt to handle multiple threads reading from the
-    # queue in parallel: they should all get StopIterations.
+    # catch attempts to 'put' more data onto the queue after it has finished.
+    finished = False
+
+    # Handle multiple threads reading from the
+    # queue in parallel: once the sentinel has been received by any thread
+    # all further attempts to read get StopIterations.
     stopped = False
 
     class SENTINEL:
@@ -27,6 +31,7 @@ class SENTINEL:
 
     def finish(self):
         self.put(self.SENTINEL)
+        self.finished = True
 
     def __iter__(self):
         return self
@@ -47,13 +52,8 @@ def __next__(self):
             raise StopIteration
         return val
 
-    def get(self, block=True, timeout=None):
-        if self.stopped:
-            raise ValueError("SentinelQueue stopped")
-        return super().get(block, timeout)
-
     def put(self, item, block=True, timeout=None):
-        if self.stopped:
+        if self.finished:
             raise ValueError("SentinelQueue stopped")
         super().put(item, block, timeout)
 
@@ -83,7 +83,7 @@ def __init__(self, name, plugin=None, config=None, position=None, notes=None, so
         self.name = name
         self.plugin = plugin
         self.config = config or []
-        self.position = position
+        self.position = position or (0.5, 0.5)
         self.sort_column = sort_column
         self.sort_descending = sort_descending
         self.notes = notes
@@ -237,34 +237,16 @@ def del_parent(self, parent):
         parent.child_nodes.discard(self)
         self.mark_dirty()
 
-    def has_sibling(self):
-        return any(len(pn.child_nodes) > 1 for pn in self.parent_nodes)
-
     def configure_plugin(self, key, value, base_dir="."):
         self.plugin.set_parameter(key, value, base_dir)
         self.mark_dirty()
 
-    def final_descendants(self):
-        if self.child_nodes:
-            return set(n2 for n1 in self.child_nodes for n2 in n1.final_descendants())
-        else:
-            return set(self)
-
-    def detatch(self):
+    def detach(self):
         for parent_node in self.parent_nodes:
             parent_node.child_nodes.discard(self)
         for child_node in self.child_nodes:
             child_node.parent_nodes.discard(self)
 
-    @classmethod
-    def get_ancestor_list(cls, nodes):
-        """Given a bunch of nodes, find the list of all the ancestors in a
-        sensible order"""
-        parents = set((p for n in nodes for p in n.parent_nodes))
-        if not parents:
-            return list(nodes)
-        return cls.get_ancestor_list(parents) + list(nodes)
-
 
 class PipelineGraph:
     def __init__(self):
@@ -285,7 +267,7 @@ def add_node(self, node):
         self.nodes.append(node)
 
     def del_node(self, node):
-        node.detatch()
+        node.detach()
         self.nodes.remove(node)
 
     def traverse_nodes(self):
diff --git a/docs/contributing/index.md b/docs/contributing/index.md
index bda5e9c..9d71bd5 100644
--- a/docs/contributing/index.md
+++ b/docs/contributing/index.md
@@ -152,6 +152,9 @@ For issues with these pages, especially accessibility issues, please
 ## Deployment
 
 Github actions are set up to run code checks and tests on every push.
+Tests are run across Python 3.9, 3.10, 3.11 and 3.12.  Even though
+3.9 is very old it is very widely deployed and there are a lot of
+small but breaking changes.
 
 Deployment is not yet automated.  There's a couple of small scripts
 to set a new version number in the code, documentation and git tags.
@@ -162,7 +165,8 @@ name on the command line:
 
     script/set_version 1.2.3
 
-There's also a script to automate upload to PyPI using twine.
+Releases are not yet automated.  Releases are on PyPI (not github),
+there's a script to automate upload to PyPI using twine:
 
     script/build_and_upload
 
diff --git a/tests/plugins/test_filter.py b/tests/plugins/test_filter.py
new file mode 100644
index 0000000..31e7b0f
--- /dev/null
+++ b/tests/plugins/test_filter.py
@@ -0,0 +1,26 @@
+import pandas as pd
+
+from countess.plugins.filter import FilterPlugin
+
+df1 = pd.DataFrame(
+    [
+        {"foo": 1, "bar": 2, "baz": 3},
+        {"foo": 4, "bar": 5, "baz": 6},
+        {"foo": 7, "bar": 8, "baz": 9},
+    ],
+)
+
+df2 = df1.set_index("foo")
+
+code_1 = "qux = bar + baz\n\nquux = bar * baz\n"
+
+code_2 = "bar + baz != 11"
+
+
+def test_filter_0():
+    plugin = FilterPlugin()
+    # plugin.set_parameter("drop.1", True)
+    plugin.prepare(["x"])
+
+    dfs = list(plugin.process(df1, "x"))
+    assert len(dfs) == 0
diff --git a/tests/test_pipeline.py b/tests/test_pipeline.py
new file mode 100644
index 0000000..889d681
--- /dev/null
+++ b/tests/test_pipeline.py
@@ -0,0 +1,90 @@
+import pytest
+
+from countess.core.pipeline import PipelineGraph, PipelineNode
+
+
+@pytest.fixture(name="pg")
+def fixture_pg():
+    pn0 = PipelineNode("node")
+    pn1 = PipelineNode("node")
+    pn2 = PipelineNode("node")
+    pn3 = PipelineNode("node")
+    pn4 = PipelineNode("node")
+
+    pg = PipelineGraph()
+    pg.add_node(pn0)
+    pg.add_node(pn1)
+    pg.add_node(pn2)
+    pg.add_node(pn3)
+    pg.add_node(pn4)
+
+    pn4.add_parent(pn2)
+    pn4.add_parent(pn3)
+    pn3.add_parent(pn1)
+    pn2.add_parent(pn1)
+    pn1.add_parent(pn0)
+    pn1.add_parent(pn0)
+
+    return pg
+
+
+def test_ancestor_descendant(pg):
+    pns = list(pg.traverse_nodes())
+    for pn in pns[1:]:
+        assert pns[0].is_ancestor_of(pn)
+        assert not pn.is_ancestor_of(pns[0])
+
+    for pn in pns[:-1]:
+        assert pns[-1].is_descendant_of(pn)
+        assert not pn.is_descendant_of(pns[-1])
+
+
+def test_pipeline_graph_tidy(pg):
+    pg.tidy()
+
+    pns = list(pg.traverse_nodes())
+
+    # check that all nodes have different positions
+    assert len(set(pn.position for pn in pns)) == len(pns)
+
+    # check that first coordinate is monotonic increasing
+    xs = [pn.position[0] for pn in pns]
+    assert sorted(xs) == xs
+
+
+def test_pipeline_del_node(pg):
+    pns = list(pg.traverse_nodes())
+    pg.del_node(pns[2])
+
+    assert not pns[2].is_descendant_of(pns[0])
+    assert not pns[2].is_ancestor_of(pns[-1])
+
+
+def test_pipeline_del_parent(pg):
+    pns = list(pg.traverse_nodes())
+    pns[2].del_parent(pns[1])
+
+    assert not pns[1].is_ancestor_of(pns[2])
+    assert pns[2].is_ancestor_of(pns[-1])
+
+
+def test_pipeline_graph_reset_node_name(pg):
+    pns = list(pg.traverse_nodes())
+    pg.reset_node_name(pns[1])
+    assert pns[1].name == "node 2"
+
+    pg.reset_node_name(pns[3])
+    assert pns[3].name == "node 4"
+
+
+def test_pipeline_graph_reset_node_names(pg):
+    pg.reset_node_names()
+    names = [pn.name for pn in pg.traverse_nodes()]
+    assert sorted(set(names)) == names
+
+
+def test_pg_reset(pg):
+    pg.reset()
+
+    assert all(pn.result is None for pn in pg.traverse_nodes())
+    assert all(pn.is_dirty for pn in pg.traverse_nodes())