pickaxe tests: add test for diffgrep_consume() internals

In diffgrep_consume() we generate a diff, and then advance past the
"+" or "-" at the start of the line for matching. This has been done
ever since the code was added in f506b8e (git log/diff: add
-G<regexp> that greps in the patch text, 2010-08-23).

If we match "line" instead of "line + 1" no tests fail, i.e. we've got
zero coverage for whether any of our searches match the beginning of
the line or not. Let's add a test for this.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

t/t4209-log-pickaxe.sh

@@ -106,6 +106,21 @@ test_expect_success 'log -S --no-textconv (missing textconv tool)' '
 	rm .gitattributes
 '
 
+test_expect_success 'setup log -[GS] plain' '
+	test_create_repo GS-plain &&
+	test_commit -C GS-plain --append A data.txt "a" &&
+	test_commit -C GS-plain --append B data.txt "a a" &&
+	test_commit -C GS-plain C data.txt "" &&
+	git -C GS-plain log >full-log
+'
+
+test_expect_success 'log -G trims diff new/old [-+]' '
+	git -C GS-plain log -G"[+-]a" >log &&
+	test_must_be_empty log &&
+	git -C GS-plain log -G"^a" >log &&
+	test_cmp log full-log
+'
+
 test_expect_success 'setup log -[GS] binary & --text' '
 	test_create_repo GS-bin-txt &&
 	test_commit -C GS-bin-txt --printf A data.bin "a\na\0a\n" &&