diff --git a/tests/test-lfs-largefiles.t b/tests/test-lfs-largefiles.t
new file mode 100644
--- /dev/null
+++ b/tests/test-lfs-largefiles.t
@@ -0,0 +1,355 @@
+This tests the interaction between the largefiles and lfs extensions, and
+conversion from largefiles -> lfs.
+
+ $ cat >> $HGRCPATH << EOF
+ > [extensions]
+ > largefiles =
+ >
+ > [lfs]
+ > # standin files are 41 bytes. Stay bigger for clarity.
+ > threshold = 42
+ > EOF
+
+Setup a repo with a normal file and a largefile, above and below the lfs
+threshold to test lfconvert. *.txt start life as a normal file; *.bin start as
+an lfs/largefile.
+
+ $ hg init largefiles
+ $ cd largefiles
+ $ echo 'normal' > normal.txt
+ $ echo 'normal above lfs threshold 0000000000000000000000000' > lfs.txt
+ $ hg ci -Am 'normal.txt'
+ adding lfs.txt
+ adding normal.txt
+ $ echo 'largefile' > large.bin
+ $ echo 'largefile above lfs threshold 0000000000000000000000' > lfs.bin
+ $ hg add --large large.bin lfs.bin
+ $ hg ci -m 'add largefiles'
+
+ $ cat >> $HGRCPATH << EOF
+ > [extensions]
+ > lfs =
+ > EOF
+
+Add an lfs file and normal file that collide with files on the other branch.
+large.bin is added as a normal file, and is named as such only to clash with the
+largefile on the other branch.
+
+ $ hg up -q '.^'
+ $ echo 'below lfs threshold' > large.bin
+ $ echo 'lfs above the lfs threshold for length 0000000000000' > lfs.bin
+ $ hg ci -Am 'add with lfs extension'
+ adding large.bin
+ adding lfs.bin
+ created new head
+
+ $ hg log -G
+ @ changeset: 2:e989d0fa3764
+ | tag: tip
+ | parent: 0:29361292f54d
+ | user: test
+ | date: Thu Jan 01 00:00:00 1970 +0000
+ | summary: add with lfs extension
+ |
+ | o changeset: 1:6513aaab9ca0
+ |/ user: test
+ | date: Thu Jan 01 00:00:00 1970 +0000
+ | summary: add largefiles
+ |
+ o changeset: 0:29361292f54d
+ user: test
+ date: Thu Jan 01 00:00:00 1970 +0000
+ summary: normal.txt
+
+--------------------------------------------------------------------------------
+Merge largefiles into lfs branch
+
+The largefiles extension will prompt to use the normal or largefile when merged
+into the lfs files. `hg manifest` will show standins if present. They aren't,
+because largefiles merge doesn't merge content. If it did, selecting (n)ormal
+would convert to lfs on commit, if appropriate.
+
+BUG: Largefiles isn't running the merge tool, like when two lfs files are
+merged. This is probably by design, but it should probably at least prompt if
+content should be taken from (l)ocal or (o)ther as well.
+
+ $ hg --config ui.interactive=True merge 6513aaab9ca0 <<EOF
+ > n
+ > n
+ > EOF
+ remote turned local normal file large.bin into a largefile
+ use (l)argefile or keep (n)ormal file? n
+ remote turned local normal file lfs.bin into a largefile
+ use (l)argefile or keep (n)ormal file? n
+ 0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+ (branch merge, don't forget to commit)
+ $ hg ci -m 'merge lfs with largefiles -> normal'
+ $ hg manifest
+ large.bin
+ lfs.bin
+ lfs.txt
+ normal.txt
+
+The merged lfs.bin resolved to lfs because the (n)ormal option was picked. The
+lfs.txt file is unchanged by the merge, because it was added before lfs was
+enabled, and the content didn't change.
+ $ hg debugdata lfs.bin 0
+ version https://git-lfs.github.com/spec/v1
+ oid sha256:81c7492b2c05e130431f65a87651b54a30c5da72c99ce35a1e9b9872a807312b
+ size 53
+ x-is-binary 0
+ $ hg debugdata lfs.txt 0
+ normal above lfs threshold 0000000000000000000000000
+
+Another filelog entry is NOT made by the merge, so nothing is committed as lfs.
+ $ hg log -r . -T '{join(lfs_files, ", ")}\n'
+
+
+Replay the last merge, but pick (l)arge this time. The manifest will show any
+standins.
+
+ $ hg up -Cq e989d0fa3764
+
+ $ hg --config ui.interactive=True merge 6513aaab9ca0 <<EOF
+ > l
+ > l
+ > EOF
+ remote turned local normal file large.bin into a largefile
+ use (l)argefile or keep (n)ormal file? l
+ remote turned local normal file lfs.bin into a largefile
+ use (l)argefile or keep (n)ormal file? l
+ getting changed largefiles
+ 2 largefiles updated, 0 removed
+ 2 files updated, 0 files merged, 2 files removed, 0 files unresolved
+ (branch merge, don't forget to commit)
+ $ hg ci -m 'merge lfs with largefiles -> large'
+ created new head
+ $ hg manifest
+ .hglf/large.bin
+ .hglf/lfs.bin
+ lfs.txt
+ normal.txt
+
+--------------------------------------------------------------------------------
+Merge lfs into largefiles branch
+
+ $ hg up -Cq 6513aaab9ca0
+ $ hg --config ui.interactive=True merge e989d0fa3764 <<EOF
+ > n
+ > n
+ > EOF
+ remote turned local largefile large.bin into a normal file
+ keep (l)argefile or use (n)ormal file? n
+ remote turned local largefile lfs.bin into a normal file
+ keep (l)argefile or use (n)ormal file? n
+ getting changed largefiles
+ 0 largefiles updated, 0 removed
+ 2 files updated, 0 files merged, 2 files removed, 0 files unresolved
+ (branch merge, don't forget to commit)
+ $ hg ci -m 'merge largefiles with lfs -> normal'
+ created new head
+ $ hg manifest
+ large.bin
+ lfs.bin
+ lfs.txt
+ normal.txt
+
+The merged lfs.bin got converted to lfs because the (n)ormal option was picked.
+The lfs.txt file is unchanged by the merge, because it was added before lfs was
+enabled.
+ $ hg debugdata lfs.bin 0
+ version https://git-lfs.github.com/spec/v1
+ oid sha256:81c7492b2c05e130431f65a87651b54a30c5da72c99ce35a1e9b9872a807312b
+ size 53
+ x-is-binary 0
+ $ hg debugdata lfs.txt 0
+ normal above lfs threshold 0000000000000000000000000
+
+Another filelog entry is NOT made by the merge, so nothing is committed as lfs.
+ $ hg log -r . -T '{join(lfs_files, ", ")}\n'
+
+
+Replay the last merge, but pick (l)arge this time. The manifest will show the
+standins.
+
+ $ hg up -Cq 6513aaab9ca0
+
+ $ hg --config ui.interactive=True merge e989d0fa3764 <<EOF
+ > l
+ > l
+ > EOF
+ remote turned local largefile large.bin into a normal file
+ keep (l)argefile or use (n)ormal file? l
+ remote turned local largefile lfs.bin into a normal file
+ keep (l)argefile or use (n)ormal file? l
+ 0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+ (branch merge, don't forget to commit)
+ $ hg ci -m 'merge largefiles with lfs -> large'
+ created new head
+ $ hg manifest
+ .hglf/large.bin
+ .hglf/lfs.bin
+ lfs.txt
+ normal.txt
+
+--------------------------------------------------------------------------------
+
+When both largefiles and lfs are configured to add by size, the tie goes to
+largefiles since it hooks cmdutil.add() and lfs hooks the filelog write in the
+commit. By the time the commit occurs, the tracked file is smaller than the
+threshold (assuming it is > 41, so the standins don't become lfs objects).
+
+ $ yes | head -n 1048576 > large_by_size.bin
+ $ hg --config largefiles.minsize=1 ci -Am 'large by size'
+ adding large_by_size.bin as a largefile
+ $ hg manifest
+ .hglf/large.bin
+ .hglf/large_by_size.bin
+ .hglf/lfs.bin
+ lfs.txt
+ normal.txt
+
+ $ hg rm large_by_size.bin
+ $ hg ci -m 'remove large_by_size.bin'
+
+Largefiles doesn't do anything special with diff, so it falls back to diffing
+the standins. Extdiff also is standin based comparison. Diff and extdiff both
+work on the original file for lfs objects.
+
+Largefile -> lfs transition
+ $ hg diff -r 1 -r 3
+ diff -r 6513aaab9ca0 -r dcc5ce63e252 .hglf/large.bin
+ --- a/.hglf/large.bin Thu Jan 01 00:00:00 1970 +0000
+ +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
+ @@ -1,1 +0,0 @@
+ -cef9a458373df9b0743a0d3c14d0c66fb19b8629
+ diff -r 6513aaab9ca0 -r dcc5ce63e252 .hglf/lfs.bin
+ --- a/.hglf/lfs.bin Thu Jan 01 00:00:00 1970 +0000
+ +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
+ @@ -1,1 +0,0 @@
+ -557fb6309cef935e1ac2c8296508379e4b15a6e6
+ diff -r 6513aaab9ca0 -r dcc5ce63e252 large.bin
+ --- /dev/null Thu Jan 01 00:00:00 1970 +0000
+ +++ b/large.bin Thu Jan 01 00:00:00 1970 +0000
+ @@ -0,0 +1,1 @@
+ +below lfs threshold
+ diff -r 6513aaab9ca0 -r dcc5ce63e252 lfs.bin
+ --- /dev/null Thu Jan 01 00:00:00 1970 +0000
+ +++ b/lfs.bin Thu Jan 01 00:00:00 1970 +0000
+ @@ -0,0 +1,1 @@
+ +lfs above the lfs threshold for length 0000000000000
+
+lfs -> largefiles transition
+ $ hg diff -r 2 -r 6
+ diff -r e989d0fa3764 -r 95e1e80325c8 .hglf/large.bin
+ --- /dev/null Thu Jan 01 00:00:00 1970 +0000
+ +++ b/.hglf/large.bin Thu Jan 01 00:00:00 1970 +0000
+ @@ -0,0 +1,1 @@
+ +cef9a458373df9b0743a0d3c14d0c66fb19b8629
+ diff -r e989d0fa3764 -r 95e1e80325c8 .hglf/lfs.bin
+ --- /dev/null Thu Jan 01 00:00:00 1970 +0000
+ +++ b/.hglf/lfs.bin Thu Jan 01 00:00:00 1970 +0000
+ @@ -0,0 +1,1 @@
+ +557fb6309cef935e1ac2c8296508379e4b15a6e6
+ diff -r e989d0fa3764 -r 95e1e80325c8 large.bin
+ --- a/large.bin Thu Jan 01 00:00:00 1970 +0000
+ +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
+ @@ -1,1 +0,0 @@
+ -below lfs threshold
+ diff -r e989d0fa3764 -r 95e1e80325c8 lfs.bin
+ --- a/lfs.bin Thu Jan 01 00:00:00 1970 +0000
+ +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
+ @@ -1,1 +0,0 @@
+ -lfs above the lfs threshold for length 0000000000000
+
+A largefiles repo can be converted to lfs. The lfconvert command uses the
+convert extension under the hood with --to-normal. So the --config based
+parameters are available, but not --authormap, --branchmap, etc.
+
+XXX: The default configitems are registered in convert.__init__, and I have no
+idea how to load that before lfconvert starts using other convert modules and
+incurring a devel-warn. Even if the convert extension is enabled on the command
+line, it complains. I have no idea how this fails, and the test in fcd2f9b06629
+works.
+
+ $ cd ..
+ $ hg lfconvert --to-normal largefiles nolargefiles 2>&1 | grep -v 'devel-warn'
+ initializing destination nolargefiles
+ 0 additional largefiles cached
+ scanning source...
+ sorting...
+ converting...
+ 8 normal.txt
+ 7 add largefiles
+ 6 add with lfs extension
+ 5 merge lfs with largefiles -> normal
+ 4 merge lfs with largefiles -> large
+ 3 merge largefiles with lfs -> normal
+ 2 merge largefiles with lfs -> large
+ 1 large by size
+ 0 remove large_by_size.bin
+ $ cd nolargefiles
+
+BUG: This should have a requires line for 'lfs'
+
+ $ cat .hg/requires
+ dotencode
+ fncache
+ generaldelta
+ revlogv1
+ store
+ $ hg log -r 'all()' -G -T '{rev} {join(lfs_files, ", ")} ({desc})\n'
+ o 8 (remove large_by_size.bin)
+ |
+ o 7 large_by_size.bin (large by size)
+ |
+ o 6 (merge largefiles with lfs -> large)
+ |\
+ +---o 5 (merge largefiles with lfs -> normal)
+ | |/
+ +---o 4 lfs.bin (merge lfs with largefiles -> large)
+ | |/
+ +---o 3 (merge lfs with largefiles -> normal)
+ | |/
+ | o 2 lfs.bin (add with lfs extension)
+ | |
+ o | 1 lfs.bin (add largefiles)
+ |/
+ o 0 lfs.txt (normal.txt)
+
+ $ hg debugdata lfs.bin 0
+ version https://git-lfs.github.com/spec/v1
+ oid sha256:2172a5bd492dd41ec533b9bb695f7691b6351719407ac797f0ccad5348c81e62
+ size 53
+ x-is-binary 0
+ $ hg debugdata lfs.bin 1
+ version https://git-lfs.github.com/spec/v1
+ oid sha256:81c7492b2c05e130431f65a87651b54a30c5da72c99ce35a1e9b9872a807312b
+ size 53
+ x-is-binary 0
+ $ hg debugdata lfs.bin 2
+ version https://git-lfs.github.com/spec/v1
+ oid sha256:2172a5bd492dd41ec533b9bb695f7691b6351719407ac797f0ccad5348c81e62
+ size 53
+ x-is-binary 0
+ $ hg debugdata lfs.bin 3
+ abort: invalid revision identifier 3
+ [255]
+
+No diffs when comparing merge and p1 that kept p1's changes. Diff of lfs to
+largefiles no longer operates in standin files.
+
+ $ hg diff -r 2:3
+ $ hg diff -r 2:6
+ diff -r e989d0fa3764 -r 752e3a0d8488 large.bin
+ --- a/large.bin Thu Jan 01 00:00:00 1970 +0000
+ +++ b/large.bin Thu Jan 01 00:00:00 1970 +0000
+ @@ -1,1 +1,1 @@
+ -below lfs threshold
+ +largefile
+ diff -r e989d0fa3764 -r 752e3a0d8488 lfs.bin
+ --- a/lfs.bin Thu Jan 01 00:00:00 1970 +0000
+ +++ b/lfs.bin Thu Jan 01 00:00:00 1970 +0000
+ @@ -1,1 +1,1 @@
+ -lfs above the lfs threshold for length 0000000000000
+ +largefile above lfs threshold 0000000000000000000000