diff --git a/tests/notcapable b/tests/notcapable
new file mode 100644
--- /dev/null
+++ b/tests/notcapable
@@ -0,0 +1,19 @@
+# Disable the $CAP wire protocol capability.
+
+if test -z "$CAP"
+then
+    echo "CAP environment variable not set."
+fi
+
+cat > notcapable-$CAP.py << EOF
+from mercurial import extensions, repo
+def extsetup():
+    extensions.wrapfunction(repo.repository, 'capable', wrapper)
+def wrapper(orig, self, name, *args, **kwargs):
+    if name == '$CAP':
+        return False
+    return orig(self, name, *args, **kwargs)
+EOF
+
+echo '[extensions]' >> $HGRCPATH
+echo "notcapable-$CAP = `pwd`/notcapable-$CAP.py" >> $HGRCPATH
diff --git a/tests/test-push-http.t b/tests/test-push-http.t
--- a/tests/test-push-http.t
+++ b/tests/test-push-http.t
@@ -68,17 +68,8 @@ expect success
 
 expect success, server lacks the unbundlehash capability
 
-  $ cat > unbundlehash-off.py << EOF
-  > from mercurial import extensions, repo
-  > def extsetup():
-  >     extensions.wrapfunction(repo.repository, 'capable', wrapper)
-  > def wrapper(orig, self, name, *args, **kwargs):
-  >     if name == 'unbundlehash':
-  >         return False
-  >     return orig(self, name, *args, **kwargs)
-  > EOF
-  $ echo '[extensions]' >> .hg/hgrc
-  $ echo "unbundlehash-off = `pwd`/unbundlehash-off.py" >> .hg/hgrc
+  $ CAP=unbundlehash
+  $ . "$TESTDIR/notcapable"
   $ req
   pushing to http://localhost:$HGPORT/
   searching for changes