tests: add script to disable a selected wire protocol capability

This can be used to test that the client and server both fall back to the
previous wire protocol when the capability is not supported.

It is currently used by test-push-http.t and I plan to use it for the HTTP
long argument support tests.

tests/notcapable

@@ -0,0 +1,19 b''
+# 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

tests/test-push-http.t

@@ -68,17 +68,8 b' 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