grep: Add basic tests

This modest patch adds simple tests for git grep -P/--perl-regexp and
its interoperation with -i and -w.

Tests are only enabled when prerequisite LIBPCRE is defined (it's
automatically set based on USE_LIBPCRE in test-lib.sh).

Signed-off-by: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/README

@@ -587,6 +587,11 @@ use these, and "test_set_prereq" for how to define your own.
    Test is not run by root user, and an attempt to write to an
    unwritable file is expected to fail correctly.
 
+ - LIBPCRE
+
+   Git was compiled with USE_LIBPCRE=YesPlease. Wrap any tests
+   that use git-grep --perl-regexp or git-grep -P in these.
+
 Tips for Writing Tests
 ----------------------
 

t/t7810-grep.sh

@@ -26,6 +26,12 @@ test_expect_success setup '
 		echo foo mmap bar_mmap
 		echo foo_mmap bar mmap baz
 	} >file &&
+	{
+		echo Hello world
+		echo HeLLo world
+		echo Hello_world
+		echo HeLLo_world
+	} >hello_world &&
 	echo vvv >v &&
 	echo ww w >w &&
 	echo x x xx x >x &&
@@ -599,4 +605,36 @@ test_expect_success 'grep -e -- -- path' '
 	test_cmp expected actual
 '
 
+cat >expected <<EOF
+hello.c:int main(int argc, const char **argv)
+hello.c:	printf("Hello world.\n");
+EOF
+
+test_expect_success LIBPCRE 'grep --perl-regexp pattern' '
+	git grep --perl-regexp "\p{Ps}.*?\p{Pe}" hello.c >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success LIBPCRE 'grep -P pattern' '
+	git grep -P "\p{Ps}.*?\p{Pe}" hello.c >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success LIBPCRE 'grep -P -i pattern' '
+	{
+		echo "hello.c:	printf(\"Hello world.\n\");"
+	} >expected &&
+	git grep -P -i "PRINTF\([^\d]+\)" hello.c >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success LIBPCRE 'grep -P -w pattern' '
+	{
+		echo "hello_world:Hello world"
+		echo "hello_world:HeLLo world"
+	} >expected &&
+	git grep -P -w "He((?i)ll)o" hello_world >actual &&
+	test_cmp expected actual
+'
+
 test_done

t/test-lib.sh

@@ -1067,6 +1067,7 @@ esac
 
 test -z "$NO_PERL" && test_set_prereq PERL
 test -z "$NO_PYTHON" && test_set_prereq PYTHON
+test -n "$USE_LIBPCRE" && test_set_prereq LIBPCRE
 
 # Can we rely on git's output in the C locale?
 if test -n "$GETTEXT_POISON"