tests: Make sure that git does not access $HOME

With the latest changes to prevent git from accessing configuration
files that it should not, it's important to be sure that we won't
have further breakage in the future.

Use strace to implement a test to make sure cgit does not access()
anything built from $HOME.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tests/t0109-gitconfig.sh

@@ -0,0 +1,25 @@
+#!/bin/sh
+
+test_description='Ensure that git does not access $HOME'
+. ./setup.sh
+
+test -n "$(which strace 2>/dev/null)" || {
+	skip_all='Skipping access validation tests: strace not found'
+	test_done
+	exit
+}
+
+test_expect_success 'no access to $HOME' '
+	non_existant_path="/path/to/some/place/that/does/not/possibly/exist"
+	while test -d "$non_existant_path"; do
+		non_existant_path="$non_existant_path/$(date +%N)"
+	done
+	strace \
+		-E HOME="$non_existant_path" \
+		-E CGIT_CONFIG="$PWD/cgitrc" \
+		-E QUERY_STRING="url=foo/commit" \
+		-e access -f -o strace.out cgit
+	test_must_fail grep "$non_existant_path" strace.out
+'
+
+test_done