mntent_test: don't assume /proc isn't the first mount.

This test tried to be lazy and test both getmntent() and getmntent_r()
in the same test, but that led to an implicit assumption that /proc
isn't the first mount returned.

This new version is quite a bit more thorough than the old. It does
assume that the mount list doesn't change while the test is running, but
that seems like a reasonable assumption to make during CTS?

Bug: https://issuetracker.google.com/230228681
Test: treehugger
Change-Id: I5c5f0b86ae1c4df9a2ce69d48e1c3accb42c687b
(cherry picked from commit 1e393b0699745d6120d2fd43f58dc3d5863e3b87)

1 files changed, 23 insertions, 7 deletions

diff --git a/tests/mntent_test.cpp b/tests/mntent_test.cpp
index b86af9fb6..4b8fc9a80 100644
--- a/tests/mntent_test.cpp
+++ b/tests/mntent_test.cpp
@@ -19,24 +19,40 @@
 #include <mntent.h>
 
 TEST(mntent, mntent_smoke) {
+  // Read all the entries with getmntent().
   FILE* fp = setmntent("/proc/mounts", "r");
   ASSERT_TRUE(fp != nullptr);
 
-  ASSERT_TRUE(getmntent(fp) != nullptr);
+  std::vector<std::string> fsnames;
+  std::vector<std::string> dirs;
+  mntent* me;
+  while ((me = getmntent(fp)) != nullptr) {
+    fsnames.push_back(me->mnt_fsname);
+    dirs.push_back(me->mnt_dir);
+  }
+
+  ASSERT_EQ(1, endmntent(fp));
 
-  bool saw_proc = false;
+  // Then again with getmntent_r(), checking they match.
+  fp = setmntent("/proc/mounts", "r");
+  ASSERT_TRUE(fp != nullptr);
 
   struct mntent entry;
   char buf[BUFSIZ];
+  size_t i = 0;
   while (getmntent_r(fp, &entry, buf, sizeof(buf)) != nullptr) {
-    if (strcmp(entry.mnt_fsname, "proc") == 0 && strcmp(entry.mnt_dir, "/proc") == 0) {
-      saw_proc = true;
-    }
+    ASSERT_EQ(fsnames[i], entry.mnt_fsname);
+    ASSERT_EQ(dirs[i], entry.mnt_dir);
+    i++;
   }
 
-  ASSERT_TRUE(saw_proc);
-
   ASSERT_EQ(1, endmntent(fp));
+
+  // And just for good measure: we did see a /proc entry, right?
+  auto it = std::find(fsnames.begin(), fsnames.end(), "proc");
+  ASSERT_TRUE(it != fsnames.end());
+  size_t proc_index = it - fsnames.begin();
+  ASSERT_EQ("/proc", dirs[proc_index]);
 }
 
 TEST(mntent, hasmntopt) {