You need one leading space more (also true for the following a/b-lines), otherwise
`cd src/testdir && make clean && TESTNUM=104 make` fails.
```diff
+  a                     #1
```
As a note: You can prevent such errors, if you copy the lines from the diff of the vim repo (in this case `hg export 5770 > patch-229`) and just remove the leading `+`.