Add tests for naive disjoint-set class and remove unused method.

python/lsst/daf/butler/queries/overlaps.py

@@ -63,27 +63,6 @@ def __init__(self, superset: Iterable[_T]):
         self._subsets = [{k} for k in superset]
         self._subsets.sort(key=len, reverse=True)
 
-    def add(self, k: _T) -> bool:  # numpydoc ignore=PR04
-        """Add a new element as its own single-element subset unless it is
-        already present.
-
-        Parameters
-        ----------
-        k
-            Value to add.
-
-        Returns
-        -------
-        added : `bool`:
-            `True` if the value was actually added, `False` if it was already
-            present.
-        """
-        for subset in self._subsets:
-            if k in subset:
-                return False
-        self._subsets.append({k})
-        return True
-
     def merge(self, a: _T, b: _T) -> bool:  # numpydoc ignore=PR04
         """Merge the subsets containing the given elements.
 

tests/test_query_utilities.py

@@ -39,7 +39,7 @@
 from lsst.daf.butler.dimensions import DimensionElement, DimensionGroup
 from lsst.daf.butler.queries import tree as qt
 from lsst.daf.butler.queries.expression_factory import ExpressionFactory
-from lsst.daf.butler.queries.overlaps import OverlapsVisitor
+from lsst.daf.butler.queries.overlaps import OverlapsVisitor, _NaiveDisjointSet
 from lsst.daf.butler.queries.visitors import PredicateVisitFlags
 from lsst.sphgeom import Mq3cPixelization, Region
 
@@ -466,5 +466,21 @@ def test_one_temporal_family(self) -> None:
     # trivially duplicates the spatial-join logic.
 
 
+class NaiveDisjointSetTestCase(unittest.TestCase):
+    """Test the naive disjoint-set implementation that backs automatic overlap
+    join creation.
+    """
+
+    def test_naive_disjoint_set(self) -> None:
+        s = _NaiveDisjointSet(range(8))
+        self.assertCountEqual(s.subsets(), [{n} for n in range(8)])
+        s.merge(3, 4)
+        self.assertCountEqual(s.subsets(), [{0}, {1}, {2}, {3, 4}, {5}, {6}, {7}])
+        s.merge(2, 1)
+        self.assertCountEqual(s.subsets(), [{0}, {1, 2}, {3, 4}, {5}, {6}, {7}])
+        s.merge(1, 3)
+        self.assertCountEqual(s.subsets(), [{0}, {1, 2, 3, 4}, {5}, {6}, {7}])
+
+
 if __name__ == "__main__":
     unittest.main()