Add split miner implementation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_empty_log.py

@@ -0,0 +1,67 @@
+# Split Miner - BPMN process discovery from event logs.
+# Authors:
+#   imacat@mail.imacat.idv.tw (imacat), 2026/3/10
+# AI assistance: Claude Code (Anthropic)
+
+# Copyright (c) 2026 imacat.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.  See the License for the specific language governing
+# permissions and limitations under the License.
+"""Tests for empty and minimal event logs.
+
+Verifies proper error handling when input data is
+insufficient for the Split Miner pipeline.
+"""
+from __future__ import annotations
+
+import unittest
+
+from split_miner import split_miner
+from split_miner.bpmn import Node, Task
+from split_miner.dfg import DirectlyFollowsGraph
+
+
+class TestEmptyLog(unittest.TestCase):
+    """Tests for empty event log handling."""
+
+    def test_empty_log_dfg(self) -> None:
+        """Empty log produces a DFG with no nodes."""
+        dfg: DirectlyFollowsGraph = (
+            DirectlyFollowsGraph({})
+        )
+        self.assertEqual(dfg.nodes, set())
+        self.assertEqual(dfg.edges, set())
+
+    def test_empty_log_no_sources(self) -> None:
+        """Empty DFG has no sources."""
+        dfg: DirectlyFollowsGraph = (
+            DirectlyFollowsGraph({})
+        )
+        self.assertEqual(dfg.sources, set())
+
+    def test_empty_log_split_miner(self) -> None:
+        """Split Miner handles empty log gracefully."""
+        model = split_miner({})
+        self.assertEqual(len(model.edges), 0)
+
+    def test_single_event_trace(self) -> None:
+        """Single-event trace produces no edges."""
+        a: Task = Task("a", "a")
+        dfg: DirectlyFollowsGraph = (
+            DirectlyFollowsGraph({(a,): 1})
+        )
+        self.assertEqual(dfg.nodes, {a})
+        self.assertEqual(dfg.edges, set())
+
+
+if __name__ == "__main__":
+    unittest.main()