[tests] Fail component test merge on conflicting duplicate IDs (#16795)

tests/script/test_merge_component_configs.py

@@ -0,0 +1,72 @@
+"""Unit tests for script/merge_component_configs.py deduplication."""
+
+from pathlib import Path
+import sys
+
+import pytest
+
+# Add the script directory to Python path so we can import the module
+sys.path.insert(0, str((Path(__file__).parent / ".." / ".." / "script").resolve()))
+
+import merge_component_configs  # noqa: E402
+
+deduplicate_by_id = merge_component_configs.deduplicate_by_id
+
+
+def test_identical_duplicate_ids_collapse() -> None:
+    """Two identical items sharing an id collapse to one without error."""
+    data = {
+        "sensor": [
+            {"id": "shared", "platform": "template", "name": "A"},
+            {"id": "shared", "platform": "template", "name": "A"},
+        ]
+    }
+    result = deduplicate_by_id(data)
+    assert result["sensor"] == [{"id": "shared", "platform": "template", "name": "A"}]
+
+
+def test_conflicting_duplicate_ids_raise() -> None:
+    """Two different items sharing an id is a hard error naming the id."""
+    data = {
+        "sensor": [
+            {"id": "dup", "platform": "template", "name": "A"},
+            {"id": "dup", "platform": "template", "name": "B"},
+        ]
+    }
+    with pytest.raises(ValueError, match="dup"):
+        deduplicate_by_id(data)
+
+
+def test_intentionally_shared_id_does_not_raise() -> None:
+    """Allowlisted singleton ids may differ across components and collapse."""
+    shared = next(iter(merge_component_configs.INTENTIONALLY_SHARED_IDS))
+    data = {
+        "time": [
+            {"id": shared, "platform": "sntp"},
+            {"id": shared, "platform": "sntp", "servers": ["a"]},
+        ]
+    }
+    result = deduplicate_by_id(data)
+    # First occurrence wins, no error raised
+    assert result["time"] == [{"id": shared, "platform": "sntp"}]
+
+
+def test_items_without_id_are_preserved() -> None:
+    """Items lacking an id are passed through untouched."""
+    data = {"binary_sensor": [{"platform": "gpio"}, {"platform": "gpio"}]}
+    result = deduplicate_by_id(data)
+    assert result["binary_sensor"] == [{"platform": "gpio"}, {"platform": "gpio"}]
+
+
+def test_nested_lists_are_checked() -> None:
+    """Conflicts nested inside dict values are also detected."""
+    data = {
+        "wrapper": {
+            "sensor": [
+                {"id": "dup", "value": 1},
+                {"id": "dup", "value": 2},
+            ]
+        }
+    }
+    with pytest.raises(ValueError, match="dup"):
+        deduplicate_by_id(data)