Avoid empty ranges vector with subsequent zero element access

db/db_table_properties_test.cc

@@ -92,6 +92,10 @@ TablePropertiesCollection
 DBTablePropertiesTest::TestGetPropertiesOfTablesInRange(
     std::vector<Range> ranges, std::size_t* num_properties,
     std::size_t* num_files) {
+
+  // Since we deref zero element in the vector it can not be empty
+  // otherwise we pass an address to some random memory
+  EXPECT_GT(ranges.size(), 0U);
   // run the query
   TablePropertiesCollection props;
   EXPECT_OK(db_->GetPropertiesOfTablesInRange(
@@ -101,10 +105,10 @@ DBTablePropertiesTest::TestGetPropertiesOfTablesInRange(
   // only which fall within requested ranges
   std::vector<LiveFileMetaData> vmd;
   db_->GetLiveFilesMetaData(&vmd);
-  for (auto md : vmd) {
+  for (auto& md : vmd) {
     std::string fn = md.db_path + md.name;
     bool in_range = false;
-    for (auto r : ranges) {
+    for (auto& r : ranges) {
       // smallestkey < limit && largestkey >= start
       if (r.limit.compare(md.smallestkey) >= 0 &&
           r.start.compare(md.largestkey) <= 0) {
@@ -187,11 +191,20 @@ TEST_F(DBTablePropertiesTest, GetPropertiesOfTablesInRange) {
   for (int j = 0; j < 100; j++) {
     // create a bunch of ranges
     std::vector<std::string> random_keys;
-    auto n = 2 * rnd.Uniform(50);
+    // Random returns numbers with zero included
+    // when we pass empty ranges TestGetPropertiesOfTablesInRange()
+    // derefs random memory in the empty ranges[0]
+    // so want to be greater than zero and even since
+    // the below loop requires that random_keys.size() to be even.
+    auto n = 2 * (rnd.Uniform(50) + 1);
+
     for (uint32_t i = 0; i < n; ++i) {
       random_keys.push_back(test::RandomKey(&rnd, 5));
     }
 
+    ASSERT_GT(random_keys.size(), 0U);
+    ASSERT_EQ((random_keys.size() % 2), 0U);
+
     std::vector<Range> ranges;
     auto it = random_keys.begin();
     while (it != random_keys.end()) {