diff --git a/src/nvim/testdir/Makefile b/src/nvim/testdir/Makefile
index dba8a8a877..0118597eb8 100644
--- a/src/nvim/testdir/Makefile
+++ b/src/nvim/testdir/Makefile
@@ -17,7 +17,6 @@ SCRIPTS := \
            test37.out             \
            test40.out             \
            test42.out             \
-           test47.out             \
            test48.out             \
            test49.out             \
            test52.out             \
@@ -33,6 +32,7 @@ SCRIPTS := \
 NEW_TESTS = \
 	    test_cscope.res \
 		test_cmdline.res \
+	    test_diffmode.res \
 	    test_hardcopy.res \
 	    test_help_tagjump.res \
 	    test_history.res \
diff --git a/src/nvim/testdir/test47.in b/src/nvim/testdir/test47.in
deleted file mode 100644
index c95c6a6850..0000000000
--- a/src/nvim/testdir/test47.in
+++ /dev/null
@@ -1,102 +0,0 @@
-Tests for vertical splits and filler lines in diff mode
-
-Also tests restoration of saved options by :diffoff.
-
-STARTTEST
-:" Disable the title to avoid xterm keeping the wrong one.
-:set notitle noicon
-/^1
-yG:new
-pkdd:w! Xtest
-ddGpkkrXoxxx:w! Xtest2
-:file Nop
-ggoyyyjjjozzzz
-:set foldmethod=marker foldcolumn=4
-:redir => nodiffsettings
-:silent! :set diff? fdm? fdc? scb? crb? wrap?
-:redir END
-:vert diffsplit Xtest
-:vert diffsplit Xtest2
-:redir => diffsettings
-:silent! :set diff? fdm? fdc? scb? crb? wrap?
-:redir END
-:let diff_fdm = &fdm
-:let diff_fdc = &fdc
-:" repeat entering diff mode here to see if this saves the wrong settings
-:diffthis
-:" jump to second window for a moment to have filler line appear at start of
-:" first window
-ggpgg:let one = winline()
-j:let one = one . "-" . winline()
-j:let one = one . "-" . winline()
-j:let one = one . "-" . winline()
-j:let one = one . "-" . winline()
-j:let one = one . "-" . winline()
-gg:let two = winline()
-j:let two = two . "-" . winline()
-j:let two = two . "-" . winline()
-j:let two = two . "-" . winline()
-j:let two = two . "-" . winline()
-gg:let three = winline()
-j:let three = three . "-" . winline()
-j:let three = three . "-" . winline()
-j:let three = three . "-" . winline()
-j:let three = three . "-" . winline()
-j:let three = three . "-" . winline()
-j:let three = three . "-" . winline()
-:call append("$", one)
-:call append("$", two)
-:call append("$", three)
-:$-2,$w! test.out
-:"
-:" Test diffoff
-:diffoff!
-1
-:let &diff = 1
-:let &fdm = diff_fdm
-:let &fdc = diff_fdc
-4
-:diffoff!
-:$put =nodiffsettings
-:$put =diffsettings
-1
-:redir => nd1
-:silent! :set diff? fdm? fdc? scb? crb? wrap?
-:redir END
-
-:redir => nd2
-:silent! :set diff? fdm? fdc? scb? crb? wrap?
-:redir END
-
-:redir => nd3
-:silent! :set diff? fdm? fdc? scb? crb? wrap?
-:redir END
-
-:$put =nd1
-:$put =nd2
-:$put =nd3
-:$-39,$w >> test.out
-:"
-:" Test that diffing shows correct filler lines
-:windo :bw!
-:enew
-:put =range(4,10)
-:1d _
-:vnew
-:put =range(1,10)
-:1d _
-:windo :diffthis
-:wincmd h
-:let w0=line('w0')
-:enew
-:put =w0
-:.w >> test.out
-:unlet! one two three nodiffsettings diffsettings diff_fdm diff_fdc nd1 nd2 nd3 w0
-:qa!
-ENDTEST
-
-1 aa
-2 bb
-3 cc
-4 dd
-5 ee
diff --git a/src/nvim/testdir/test47.ok b/src/nvim/testdir/test47.ok
deleted file mode 100644
index 83e96571ad..0000000000
--- a/src/nvim/testdir/test47.ok
+++ /dev/null
@@ -1,44 +0,0 @@
-2-4-5-6-8-9
-1-2-4-5-8
-2-3-4-5-6-7-8
-
-
-nodiff
-  foldmethod=marker
-  foldcolumn=4
-noscrollbind
-nocursorbind
-  wrap
-
-
-  diff
-  foldmethod=diff
-  foldcolumn=2
-  scrollbind
-  cursorbind
-nowrap
-
-
-nodiff
-  foldmethod=marker
-  foldcolumn=4
-noscrollbind
-nocursorbind
-  wrap
-
-
-nodiff
-  foldmethod=marker
-  foldcolumn=4
-noscrollbind
-nocursorbind
-  wrap
-
-
-nodiff
-  foldmethod=marker
-  foldcolumn=4
-noscrollbind
-nocursorbind
-  wrap
-1
diff --git a/src/nvim/testdir/test_diffmode.vim b/src/nvim/testdir/test_diffmode.vim
new file mode 100644
index 0000000000..e5d9ff94d9
--- /dev/null
+++ b/src/nvim/testdir/test_diffmode.vim
@@ -0,0 +1,165 @@
+" Tests for diff mode
+
+func Test_diff_fold_sync()
+  enew!
+  let l = range(50)
+  call setline(1, l)
+  diffthis
+  let winone = win_getid()
+  new
+  let l[25] = 'diff'
+  call setline(1, l)
+  diffthis
+  let wintwo = win_getid()
+  " line 15 is inside the closed fold
+  call assert_equal(19, foldclosedend(10))
+  call win_gotoid(winone)
+  call assert_equal(19, foldclosedend(10))
+  " open the fold
+  normal zv
+  call assert_equal(-1, foldclosedend(10))
+  " fold in other window must have opened too
+  call win_gotoid(wintwo)
+  call assert_equal(-1, foldclosedend(10))
+
+  " cursor position is in sync
+  normal 23G
+  call win_gotoid(winone)
+  call assert_equal(23, getcurpos()[1])
+
+  windo diffoff
+  close!
+  set nomodified
+endfunc
+
+func Test_vert_split()
+  " Disable the title to avoid xterm keeping the wrong one.
+  set notitle noicon
+  new
+  let l = ['1 aa', '2 bb', '3 cc', '4 dd', '5 ee']
+  call setline(1, l)
+  w! Xtest
+  normal dd
+  $
+  put
+  normal kkrXoxxx
+  w! Xtest2
+  file Nop
+  normal ggoyyyjjjozzzz
+  set foldmethod=marker foldcolumn=4
+  call assert_equal(0, &diff)
+  call assert_equal('marker', &foldmethod)
+  call assert_equal(4, &foldcolumn)
+  call assert_equal(0, &scrollbind)
+  call assert_equal(0, &cursorbind)
+  call assert_equal(1, &wrap)
+
+  vert diffsplit Xtest
+  vert diffsplit Xtest2
+  call assert_equal(1, &diff)
+  call assert_equal('diff', &foldmethod)
+  call assert_equal(2, &foldcolumn)
+  call assert_equal(1, &scrollbind)
+  call assert_equal(1, &cursorbind)
+  call assert_equal(0, &wrap)
+
+  let diff_fdm = &fdm
+  let diff_fdc = &fdc
+  " repeat entering diff mode here to see if this saves the wrong settings
+  diffthis
+  " jump to second window for a moment to have filler line appear at start of
+  " first window
+  wincmd w
+  normal gg
+  wincmd p
+  normal gg
+  call assert_equal(2, winline())
+  normal j
+  call assert_equal(4, winline())
+  normal j
+  call assert_equal(5, winline())
+  normal j
+  call assert_equal(6, winline())
+  normal j
+  call assert_equal(8, winline())
+  normal j
+  call assert_equal(9, winline())
+
+  wincmd w
+  normal gg
+  call assert_equal(1, winline())
+  normal j
+  call assert_equal(2, winline())
+  normal j
+  call assert_equal(4, winline())
+  normal j
+  call assert_equal(5, winline())
+  normal j
+  call assert_equal(8, winline())
+
+  wincmd w
+  normal gg
+  call assert_equal(2, winline())
+  normal j
+  call assert_equal(3, winline())
+  normal j
+  call assert_equal(4, winline())
+  normal j
+  call assert_equal(5, winline())
+  normal j
+  call assert_equal(6, winline())
+  normal j
+  call assert_equal(7, winline())
+  normal j
+  call assert_equal(8, winline())
+
+  " Test diffoff
+  diffoff!
+  1wincmd 2
+  let &diff = 1
+  let &fdm = diff_fdm
+  let &fdc = diff_fdc
+  4wincmd w
+  diffoff!
+  1wincmd w
+  call assert_equal(0, &diff)
+  call assert_equal('marker', &foldmethod)
+  call assert_equal(4, &foldcolumn)
+  call assert_equal(0, &scrollbind)
+  call assert_equal(0, &cursorbind)
+  call assert_equal(1, &wrap)
+
+  wincmd w
+  call assert_equal(0, &diff)
+  call assert_equal('marker', &foldmethod)
+  call assert_equal(4, &foldcolumn)
+  call assert_equal(0, &scrollbind)
+  call assert_equal(0, &cursorbind)
+  call assert_equal(1, &wrap)
+
+  wincmd w
+  call assert_equal(0, &diff)
+  call assert_equal('marker', &foldmethod)
+  call assert_equal(4, &foldcolumn)
+  call assert_equal(0, &scrollbind)
+  call assert_equal(0, &cursorbind)
+  call assert_equal(1, &wrap)
+
+  windo bw!
+endfunc
+
+func Test_filler_lines()
+  " Test that diffing shows correct filler lines
+  enew!
+  put =range(4,10)
+  1d _
+  vnew
+  put =range(1,10)
+  1d _
+  windo diffthis
+  wincmd h
+  call assert_equal(1, line('w0'))
+  unlet! diff_fdm diff_fdc
+
+  windo bw!
+endfunc
diff --git a/src/nvim/version.c b/src/nvim/version.c
index cd7b70b027..ce103ec7dd 100644
--- a/src/nvim/version.c
+++ b/src/nvim/version.c
@@ -317,7 +317,7 @@ static int included_patches[] = {
   // 2126,
   // 2125,
   // 2124,
-  // 2123,
+  2123,
   // 2122 NA
   // 2121,
   // 2120,