$ hg init repo

  $ cd repo

  $ cat > a <<EOF

  > c

  > c

  > a

  > a

  > b

  > a

  > a

  > c

  > c

  > EOF

  $ hg ci -Am adda

  adding a

  $ cat > a <<EOF

  > c

  > c

  > a

  > a

  > dd

  > a

  > a

  > c

  > c

  > EOF

default context

  $ hg diff --nodates

  diff -r cf9f4ba66af2 a

  --- a/a

  +++ b/a

  @@ -2,7 +2,7 @@

   c

   a

   a

  -b

  +dd

   a

   a

   c

invalid --unified

  $ hg diff --nodates -U foo

  abort: diff context lines count must be an integer, not 'foo'

  [255]

  $ hg diff --nodates -U 2

  diff -r cf9f4ba66af2 a

  --- a/a

  +++ b/a

  @@ -3,5 +3,5 @@

   a

   a

  -b

  +dd

   a

   a

  $ hg --config diff.unified=2 diff --nodates

  diff -r cf9f4ba66af2 a

  --- a/a

  +++ b/a

  @@ -3,5 +3,5 @@

   a

   a

  -b

  +dd

   a

   a

  $ hg diff --nodates -U 1

  diff -r cf9f4ba66af2 a

  --- a/a

  +++ b/a

  @@ -4,3 +4,3 @@

   a

  -b

  +dd

   a

invalid diff.unified

  $ hg --config diff.unified=foo diff --nodates

  abort: diff context lines count must be an integer, not 'foo'

  [255]

test off-by-one error with diff -p

  $ hg init diffp

  $ cd diffp

  $ echo a > a

  $ hg ci -Ama

  adding a

  $ rm a

  $ echo b > a

  $ echo a >> a

  $ echo c >> a

  $ hg diff -U0 -p --nodates

  diff -r cb9a9f314b8b a

  --- a/a

  +++ b/a

  @@ -1,0 +1,1 @@

  +b

  @@ -2,0 +3,1 @@ a

  +c