tests: add extension to emulate invoking internalpatch at the specific time

This extension fakes "mtime" of patched files to emulate invoking
'patch.internalpatch()' at the specific time.

This is useful to reproduce timing critical issues fixed in subsequent
patches.

tests/fakepatchtime.py

@@ -0,0 +1,26 b''
+# extension to emulate invoking 'patch.internalpatch()' at the time
+# specified by '[fakepatchtime] fakenow'
+
+from mercurial import extensions, patch as patchmod, util
+
+def internalpatch(orig, ui, repo, patchobj, strip,
+                  prefix='', files=None,
+                  eolmode='strict', similarity=0):
+    if files is None:
+        files = set()
+    r = orig(ui, repo, patchobj, strip,
+             prefix=prefix, files=files,
+             eolmode=eolmode, similarity=similarity)
+
+    fakenow = ui.config('fakepatchtime', 'fakenow')
+    if fakenow:
+        # parsing 'fakenow' in YYYYmmddHHMM format makes comparison between
+        # 'fakenow' value and 'touch -t YYYYmmddHHMM' argument easy
+        fakenow = util.parsedate(fakenow, ['%Y%m%d%H%M'])[0]
+        for f in files:
+            repo.wvfs.utime(f, (fakenow, fakenow))
+
+    return r
+
+def extsetup(ui):
+    extensions.wrapfunction(patchmod, 'internalpatch', internalpatch)