index tests: test capitalization before mkdir

tests/index/tests.c

diff --git a/tests/index/tests.c b/tests/index/tests.c
index d0372f1..a63183e 100644
--- a/tests/index/tests.c
+++ b/tests/index/tests.c
@@ -340,8 +340,10 @@
 	cl_must_pass(p_mkdir("./invalid/subdir", 0777));
 
 	/* cl_git_mkfile() needs the dir to exist */
-	cl_must_pass(p_mkdir("./invalid/.GIT", 0777));
-	cl_must_pass(p_mkdir("./invalid/.GiT", 0777));
+	if (!git_path_exists("./invalid/.GIT"))
+		cl_must_pass(p_mkdir("./invalid/.GIT", 0777));
+	if (!git_path_exists("./invalid/.GiT"))
+		cl_must_pass(p_mkdir("./invalid/.GiT", 0777));
 
 	add_invalid_filename(repo, ".git/hello");
 	add_invalid_filename(repo, ".GIT/hello");