fdtrack: add wrapper for socketpair.

Bug: https://issuetracker.google.com/154450436
Test: bionic-unit-tests
Change-Id: I8b25accf00dc01f6fab351f3ba612f6b0ff9d094
diff --git a/tests/fdtrack_test.cpp b/tests/fdtrack_test.cpp
index e58ff79..bfa3dd1 100644
--- a/tests/fdtrack_test.cpp
+++ b/tests/fdtrack_test.cpp
@@ -203,6 +203,14 @@
   fds;
 }));
 
+FDTRACK_TEST(socketpair, ({
+  std::vector<int> fds = { -1, -1};
+  if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, fds.data()) != 0) {
+    err(1, "socketpair failed");
+  }
+  fds;
+}));
+
 FDTRACK_TEST(epoll_create, epoll_create(1));
 FDTRACK_TEST(epoll_create1, epoll_create1(0));