diff --git a/tests/test-merge-combination.t b/tests/test-merge-combination.t
new file mode 100644
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+++ b/tests/test-merge-combination.t
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+This file shows what hg says are "modified" files for a merge commit
+(hg log -T {files}), somewhat exhaustively.
+It shows merges that involves files contents changing, and merges that
+involve executable bit changing, but not merges with multiple or zero
+merge ancestors, nor copies/renames, and nor identical file contents
+with different filelog revisions.
+
+genmerges is the workhorse. Given:
+- a range function describing the possible values for file a
+- a isgood function to filter out uninteresting combination
+- a createfile function to actually write the values for file a on the
+filesystem
+it print a series of lines that look like: abcd C: output of -T {files}
+describing the file a at respectively the base, p2, p1, merge
+revision. "C" indicates that hg merge had conflicts.
+  $ genmerges () {
+  >   for base in `range` -; do
+  >     for r1 in `range $base` -; do
+  >       for r2 in `range $base $r1` -; do
+  >         for m in `range $base $r1 $r2` -; do
+  >           line="$base$r1$r2$m"
+  >           isgood $line || continue
+  >           hg init repo
+  >           cd repo
+  >           make_commit () {
+  >             v=$1; msg=$2; file=$3;
+  >             if [ $v != - ]; then
+  >               createfile $v
+  >             else
+  >               if [ -f a ]
+  >               then rm a
+  >               else touch $file
+  >               fi
+  >             fi
+  >             hg commit -q -Am $msg || exit 123
+  >           }
+  >           echo foo > foo
+  >           make_commit $base base b
+  >           make_commit $r1 r1 c
+  >           hg up -r 0 -q
+  >           make_commit $r2 r2 d
+  >           hg merge -q -r 1 > ../output 2>&1
+  >           if [ $? -ne 0 ]; then rm -f *.orig; hg resolve -m --all -q; fi
+  >           if [ -s ../output ]; then conflicts=" C"; else conflicts="  "; fi
+  >           make_commit $m m e
+  >           if [ $m = $r1 ] && [ $m = $r2 ]
+  >           then expected=
+  >           elif [ $m = $r1 ]
+  >           then if [ $base = $r2 ]
+  >                then expected=
+  >                else expected=a
+  >                fi
+  >           elif [ $m = $r2 ]
+  >           then if [ $base = $r1 ]
+  >                then expected=
+  >                else expected=a
+  >                fi
+  >           else expected=a
+  >           fi
+  >           got=`hg log -r 3 --template '{files}\n' | tr --delete 'e '`
+  >           if [ "$got" = "$expected" ]
+  >           then echo "$line$conflicts: agree on \"$got\""
+  >           else echo "$line$conflicts: hg said \"$got\", expected \"$expected\""
+  >           fi
+  >           cd ../
+  >           rm -rf repo
+  >         done
+  >       done
+  >     done
+  >   done
+  > }
+
+All the merges of various file contents.
+
+  $ range () {
+  >   max=0
+  >   for i in $@; do
+  >     if [ $i = - ]; then continue; fi
+  >     if [ $i -gt $max ]; then max=$i; fi
+  >   done
+  >   $TESTDIR/seq.py `expr $max + 1`
+  > }
+  $ isgood () { true; }
+  $ createfile () {
+  >   if [ -f a ] && [ "`cat a`" = $1 ]
+  >   then touch $file
+  >   else echo $v > a
+  >   fi
+  > }
+
+  $ genmerges
+  1111  : agree on ""
+  1112  : agree on "a"
+  111-  : agree on "a"
+  1121  : agree on "a"
+  1122  : agree on ""
+  1123  : agree on "a"
+  112-  : agree on "a"
+  11-1  : hg said "", expected "a"
+  11-2  : agree on "a"
+  11--  : agree on ""
+  1211  : agree on "a"
+  1212  : agree on ""
+  1213  : agree on "a"
+  121-  : agree on "a"
+  1221  : agree on "a"
+  1222  : agree on ""
+  1223  : agree on "a"
+  122-  : agree on "a"
+  1231 C: agree on "a"
+  1232 C: agree on "a"
+  1233 C: agree on "a"
+  1234 C: agree on "a"
+  123- C: agree on "a"
+  12-1 C: agree on "a"
+  12-2 C: hg said "", expected "a"
+  12-3 C: agree on "a"
+  12-- C: agree on "a"
+  1-11  : hg said "", expected "a"
+  1-12  : agree on "a"
+  1-1-  : hg said "a", expected ""
+  1-21 C: agree on "a"
+  1-22 C: hg said "", expected "a"
+  1-23 C: agree on "a"
+  1-2- C: agree on "a"
+  1--1  : agree on "a"
+  1--2  : agree on "a"
+  1---  : agree on ""
+  -111  : agree on ""
+  -112  : agree on "a"
+  -11-  : agree on "a"
+  -121 C: agree on "a"
+  -122 C: agree on "a"
+  -123 C: agree on "a"
+  -12- C: agree on "a"
+  -1-1  : agree on ""
+  -1-2  : agree on "a"
+  -1--  : agree on "a"
+  --11  : agree on ""
+  --12  : agree on "a"
+  --1-  : agree on "a"
+  ---1  : agree on "a"
+  ----  : agree on ""
+
+All the merges of executable bit.
+
+  $ range () {
+  >   max=a
+  >   for i in $@; do
+  >     if [ $i = - ]; then continue; fi
+  >     if [ $i > $max ]; then max=$i; fi
+  >   done
+  >   if [ $max = a ]; then echo f; else echo f x; fi
+  > }
+  $ isgood () { case $line in *f*x*) true;; *) false;; esac; }
+  $ createfile () {
+  >   if [ -f a ] && (([ -x a ] && [ $v = x ]) || (! [ -x a ] && [ $v != x ]))
+  >   then touch $file
+  >   else touch a; if [ $v = x ]; then chmod +x a; else chmod -x a; fi
+  >   fi
+  > }
+
+#if execbit
+  $ genmerges
+  fffx  : agree on "a"
+  ffxf  : agree on "a"
+  ffxx  : agree on ""
+  ffx-  : agree on "a"
+  ff-x  : hg said "", expected "a"
+  fxff  : hg said "", expected "a"
+  fxfx  : hg said "a", expected ""
+  fxf-  : agree on "a"
+  fxxf  : agree on "a"
+  fxxx  : agree on ""
+  fxx-  : agree on "a"
+  fx-f  : hg said "", expected "a"
+  fx-x  : hg said "", expected "a"
+  fx--  : hg said "", expected "a"
+  f-fx  : agree on "a"
+  f-xf  : agree on "a"
+  f-xx  : hg said "", expected "a"
+  f-x-  : agree on "a"
+  f--x  : agree on "a"
+  -ffx  : agree on "a"
+  -fxf C: agree on "a"
+  -fxx C: hg said "", expected "a"
+  -fx- C: agree on "a"
+  -f-x  : hg said "", expected "a"
+  --fx  : agree on "a"
+#endif
+
+Files modified or cleanly merged, with no greatest common ancestors:
+
+  $ hg init repo; cd repo
+  $ touch a0 b0; hg commit -qAm 0
+  $ hg up -qr null; touch a1 b1; hg commit -qAm 1
+  $ hg merge -qr 0; rm b*; hg commit -qAm 2
+  $ hg log -r . -T '{files}\n'
+  b0 b1
+  $ cd ../
+  $ rm -rf repo
+
+A few cases of criss-cross merges involving deletions (listing all
+such merges is probably too much). Both gcas contain $files, so we
+expect the final merge to behave like a merge with a single gca
+containing $files.
+
+  $ hg init repo; cd repo
+  $ files="c1 u1 c2 u2"
+  $ touch $files; hg commit -qAm '0 root'
+  $ for f in $files; do echo f > $f; done; hg commit -qAm '1 gca1'
+  $ hg up -qr0; hg revert -qr 1 --all; hg commit -qAm '2 gca2'
+  $ hg up -qr 1; hg merge -qr 2; rm *1; hg commit -qAm '3 p1'
+  $ hg up -qr 2; hg merge -qr 1; rm *2; hg commit -qAm '4 p2'
+  $ hg merge -qr 3; echo f > u1; echo f > u2; rm -f c1 c2
+  $ hg commit -qAm '5 merge with two gcas'
+  $ hg log -r . -T '{files}\n' # expecting u1 u2
+  c1
+  $ cd ../
+  $ rm -rf repo