diff --stat: add a test for output with COLUMNS=40

In preparation for the introduction on the limit of the width of the
graph part, a new test with COLUMNS=40 is added to check that the
environment variable influences diff, show, log, but not format-patch.
A new test is added because limiting the graph part makes COLUMNS=200
stop influencing diff --stat behaviour, which isn't wide enough now.
The old test with COLUMNS=200 is retained to check for regressions.

Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4052-stat-output.sh

@@ -101,6 +101,25 @@ respects expect200 show --stat
 respects expect200 log -1 --stat
 EOF
 
+cat >expect40 <<'EOF'
+ abcd | 1000 ++++++++++++++++++++++++++
+EOF
+
+while read verb expect cmd args
+do
+	test_expect_success "$cmd $verb not enough COLUMNS (big change)" '
+		COLUMNS=40 git $cmd $args >output
+		grep " | " output >actual &&
+		test_cmp "$expect" actual
+	'
+done <<\EOF
+ignores expect80 format-patch -1 --stdout
+respects expect40 diff HEAD^ HEAD --stat
+respects expect40 show --stat
+respects expect40 log -1 --stat
+EOF
+
+
 cat >expect <<'EOF'
  abcd | 1000 ++++++++++++++++++++++++++
 EOF