Factor out the waiting for children in bionic tests.

Change-Id: I4a1e51b6920b33dc892d447f5bd6d10f1cb2704a
diff --git a/tests/utils.h b/tests/utils.h
index a8f3441..828c8d0 100644
--- a/tests/utils.h
+++ b/tests/utils.h
@@ -16,8 +16,11 @@
 
 #ifndef __TEST_UTILS_H
 #define __TEST_UTILS_H
+
 #include <inttypes.h>
 #include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/wait.h>
 #include <unistd.h>
 
 #include <atomic>
@@ -109,4 +112,11 @@
   }
 }
 
+static inline void AssertChildExited(int pid, int expected_exit_status) {
+  int status;
+  ASSERT_EQ(pid, waitpid(pid, &status, 0));
+  ASSERT_TRUE(WIFEXITED(status));
+  ASSERT_EQ(expected_exit_status, WEXITSTATUS(status));
+}
+
 #endif