t7002: test for not using external grep on skip-worktree paths

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-grep.c

@@ -232,6 +232,7 @@ static int exec_grep(int argc, const char **argv)
 	int status;
 
 	argv[argc] = NULL;
+	trace_argv_printf(argv, "trace: grep:");
 	pid = fork();
 	if (pid < 0)
 		return pid;

t/t7002-grep.sh

@@ -340,4 +340,16 @@ test_expect_success 'grep -p -B5' '
 	test_cmp expected actual
 '
 
+test_expect_success EXTGREP 'external grep is called' '
+	GIT_TRACE=2 git grep foo >/dev/null 2>actual &&
+	grep "trace: grep:.*foo" actual >/dev/null
+'
+
+test_expect_success EXTGREP 'no external grep when skip-worktree entries exist' '
+	git update-index --skip-worktree file &&
+	GIT_TRACE=2 git grep foo >/dev/null 2>actual &&
+	! grep "trace: grep:" actual >/dev/null &&
+	git update-index --no-skip-worktree file
+'
+
 test_done