Add assertions that BatchWrite(erase=true) erases

src/coins.cpp

@@ -250,7 +250,10 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
 
 bool CCoinsViewCache::Flush() {
     bool fOk = base->BatchWrite(cacheCoins, hashBlock, /*erase=*/true);
-    cacheCoins.clear();
+    if (fOk && !cacheCoins.empty()) {
+        /* BatchWrite must erase all cacheCoins elements when erase=true. */
+        throw std::logic_error("Not all cached coins were erased");
+    }
     cachedCoinsUsage = 0;
     return fOk;
 }