chore: add coverage exclusion for main function and test a couple more corner cases

Author: provos

src/planai/graph.py

@@ -730,7 +730,7 @@ def __repr__(self) -> str:
         return self.__str__()
 
 
-def main():
+def main():  # pragma: no cover
     import argparse
     import random
 

tests/planai/test_graph.py

@@ -64,6 +64,11 @@ def test_set_dependency_error(self):
     def test_sink_worker(self):
         worker = DummyWorker()
         self.graph.add_worker(worker)
+
+        # Cannot set a sink that is not being produced
+        with self.assertRaises(ValueError):
+            self.graph.set_sink(worker, Task)
+
         self.graph.set_sink(worker, DummyTask)
         self.assertIsNotNone(self.graph._sink_worker)
 
@@ -131,6 +136,10 @@ def consume_work(self, task: DummyTask):
         self.graph.prepare(display_terminal=False)
         self.graph.set_entry(worker)
 
+        # Try to add work for a non-entry worker
+        with self.assertRaises(ValueError):
+            self.graph.add_work(test_worker, initial_task)
+
         # Add metadata to be tracked with the task
         metadata = {"test_key": "test_value"}
         provenance = self.graph.add_work(worker, initial_task, metadata=metadata)