test-context: add test for performing a diff on a memctx

We now see the first result of all that refactoring of memctx: we can now diff
against a memctx.

tests/test-context.py

@@ -41,8 +41,12 b' def getfilectx(repo, memctx, f):'
     return context.memfilectx(repo, f, data, 'l' in flags, 'x' in flags)
 
 ctxa = repo.changectx(0)
-ctxb = context.memctx(repo, [ctxa.node(), None],
-                      "test diff",
-                      ["foo"], getfilectx)
+ctxb = context.memctx(repo, [ctxa.node(), None], "test diff", ["foo"],
+                      getfilectx, ctxa.user(), ctxa.date())
 
 print ctxb.status(ctxa)
+
+# test performing a diff on a memctx
+
+for d in ctxb.diff(ctxa, git=True):
+    print d

tests/test-context.py.out

@@ -3,3 +3,11 b' ASCII : Gr?ezi!'
 Latin-1 : Gr�ezi!
 UTF-8   : Grüezi!
 (['foo'], [], [], [], [], [], [])
+diff --git a/foo b/foo
+
+--- a/foo
++++ b/foo
+@@ -1,1 +1,2 @@
+ foo
++bar
+