--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-missing-capability.t	Mon Dec 24 14:04:16 2018 -0500
@@ -0,0 +1,46 @@
+Checking how hg behaves when one side of a pull/push doesn't support
+some capability (because it's running an older hg version, usually).
+
+  $ hg init repo1
+  $ cd repo1
+  $ echo a > a; hg add -q a; hg commit -q -m a
+  $ hg bookmark a
+  $ hg clone -q . ../repo2
+  $ cd ../repo2
+
+  $ touch $TESTTMP/disable-lookup.py
+  $ disable_cap() {
+  >   rm -f $TESTTMP/disable-lookup.pyc # pyc caching is buggy
+  >   cat <<EOF > $TESTTMP/disable-lookup.py
+  > from mercurial import extensions, wireprotov1server
+  > def wcapabilities(orig, *args, **kwargs):
+  >   cap = orig(*args, **kwargs)
+  >   cap.remove('$1')
+  >   return cap
+  > extensions.wrapfunction(wireprotov1server, '_capabilities', wcapabilities)
+  > EOF
+  > }
+  $ cat >> ../repo1/.hg/hgrc <<EOF
+  > [extensions]
+  > disable-lookup = $TESTTMP/disable-lookup.py
+  > EOF
+  $ cat >> .hg/hgrc <<EOF
+  > [ui]
+  > ssh = "$PYTHON" "$TESTDIR/dummyssh"
+  > EOF
+
+  $ hg pull ssh://user@dummy/repo1 -r tip -B a
+  pulling from ssh://user@dummy/repo1
+  no changes found
+
+  $ disable_cap lookup
+  $ hg pull ssh://user@dummy/repo1 -r tip -B a
+  pulling from ssh://user@dummy/repo1
+  abort: other repository doesn't support revision lookup, so a rev cannot be specified.
+  [255]
+
+  $ disable_cap pushkey
+  $ hg pull ssh://user@dummy/repo1 -r tip -B a
+  pulling from ssh://user@dummy/repo1
+  abort: remote bookmark a not found!
+  [255]