diff -r 3bf6979a1785 -r 006c9ce486fa tests/test-rust-ancestor.py
--- a/tests/test-rust-ancestor.py	Wed Jan 09 17:31:36 2019 +0100
+++ b/tests/test-rust-ancestor.py	Fri Nov 30 20:05:34 2018 +0100
@@ -11,7 +11,8 @@
     # this would fail already without appropriate ancestor.__package__
     from mercurial.rustext.ancestor import (
         AncestorsIterator,
-        LazyAncestors
+        LazyAncestors,
+        MissingAncestors,
     )
 
 try:
@@ -105,6 +106,22 @@
         # let's check bool for an empty one
         self.assertFalse(LazyAncestors(idx, [0], 0, False))
 
+    def testmissingancestors(self):
+        idx = self.parseindex()
+        missanc = MissingAncestors(idx, [1])
+        self.assertTrue(missanc.hasbases())
+        self.assertEqual(missanc.missingancestors([3]), [2, 3])
+        missanc.addbases({2})
+        self.assertEqual(set(missanc.bases()), {1, 2})
+        self.assertEqual(missanc.missingancestors([3]), [3])
+
+    def testmissingancestorsremove(self):
+        idx = self.parseindex()
+        missanc = MissingAncestors(idx, [1])
+        revs = {0, 1, 2, 3}
+        missanc.removeancestorsfrom(revs)
+        self.assertEqual(revs, {2, 3})
+
     def testrefcount(self):
         idx = self.parseindex()
         start_count = sys.getrefcount(idx)