new file mode 100644
--- /dev/null
+++ b/src/testdir/test_cjk_linebreak.vim
@@ -0,0 +1,91 @@
+scriptencoding utf-8
+
+func Run_cjk_linebreak_after()
+  set textwidth=12
+  for punct in [
+        \ '!', '%', ')', ',', ':', ';', '>', '?', ']', '}', '’', '”', '†', '‡',
+        \ '…', '‰', '‱', '‼', '⁇', '⁈', '⁉', '℃', '℉', '、', '。', '〉', '》',
+        \ '」', '』', '】', '〕', '〗', '〙', '〛', '！', '）', '，', '．', '：',
+        \ '；', '？', '］', '｝']
+    call setline('.', '这是一个测试'.punct.'试试 CJK 行禁则补丁。')
+    normal gqq
+    call assert_equal('这是一个测试'.punct, getline(1))
+    %d_
+  endfor
+endfunc
+
+func Test_cjk_linebreak_after()
+  set formatoptions=croqn2mB1j
+  call Run_cjk_linebreak_after()
+endfunc
+
+" TODO: this test fails
+"func Test_cjk_linebreak_after_rigorous()
+"  set formatoptions=croqn2mB1j]
+"  call Run_cjk_linebreak_after()
+"endfunc
+
+func Run_cjk_linebreak_before()
+  set textwidth=12
+  for punct in [
+        \ '(', '<', '[', '`', '{', '‘', '“', '〈', '《', '「', '『', '【', '〔',
+        \ '〖', '〘', '〚', '（', '［', '｛']
+    call setline('.', '这是个测试'.punct.'试试 CJK 行禁则补丁。')
+    normal gqq
+    call assert_equal('这是个测试', getline(1))
+    %d_
+  endfor
+endfunc
+
+func Test_cjk_linebreak_before()
+  set formatoptions=croqn2mB1j
+  call Run_cjk_linebreak_before()
+endfunc
+
+func Test_cjk_linebreak_before_rigorous()
+  set formatoptions=croqn2mB1j]
+  call Run_cjk_linebreak_before()
+endfunc
+
+func Run_cjk_linebreak_nobetween()
+  " …… must not start a line
+  call setline('.', '这是个测试……试试 CJK 行禁则补丁。')
+  set textwidth=12 ambiwidth=double
+  normal gqq
+  " TODO: this fails
+  " call assert_equal('这是个测试……', getline(1))
+  %d_
+
+  call setline('.', '这是一个测试……试试 CJK 行禁则补丁。')
+  set textwidth=12 ambiwidth=double
+  normal gqq
+  call assert_equal('这是一个测', getline(1))
+  %d_
+
+  " but —— can
+  call setline('.', '这是个测试——试试 CJK 行禁则补丁。')
+  set textwidth=12 ambiwidth=double
+  normal gqq
+  call assert_equal('这是个测试', getline(1))
+endfunc
+
+func Test_cjk_linebreak_nobetween()
+  set formatoptions=croqn2mB1j
+  call Run_cjk_linebreak_nobetween()
+endfunc
+
+func Test_cjk_linebreak_nobetween_rigorous()
+  set formatoptions=croqn2mB1j]
+  call Run_cjk_linebreak_nobetween()
+endfunc
+
+func Test_cjk_linebreak_join_punct()
+  for punct in ['——', '〗', '，', '。', '……']
+    call setline(1, '文本文本'.punct)
+    call setline(2, 'English')
+    set formatoptions=croqn2mB1j
+    normal ggJ
+    call assert_equal('文本文本'.punct.'English', getline(1))
+    %d_
+  endfor
+endfunc