Add a hasmntopt() test.

This example came up on the musl mailing list.

Change-Id: I21029c908f22ba9c073845673c3159ada6d9b3ca

Author: enh-google

tests/mntent_test.cpp

@@ -59,9 +59,7 @@ TEST(mntent, hasmntopt) {
   // indices                  1  1
   // of keys:      0    5   9 1  4
   char mnt_opts[]{"aa=b,a=b,b,bb,c=d"};
-  struct mntent ent;
-  memset(&ent, 0, sizeof(ent));
-  ent.mnt_opts = mnt_opts;
+  struct mntent ent = {.mnt_opts = mnt_opts};
 
   EXPECT_EQ(mnt_opts, hasmntopt(&ent, "aa"));
   EXPECT_EQ(mnt_opts + 5, hasmntopt(&ent, "a"));
@@ -71,3 +69,9 @@ TEST(mntent, hasmntopt) {
   EXPECT_EQ(nullptr, hasmntopt(&ent, "d"));
   EXPECT_EQ(nullptr, hasmntopt(&ent, "e"));
 }
+
+TEST(mntent, hasmntopt_no_suffix_match) {
+  char mnt_opts[]{"noatime"};
+  struct mntent ent = {.mnt_opts = mnt_opts};
+  EXPECT_EQ(nullptr, hasmntopt(&ent, "atime"));
+}