Stabilize PreparedStatementCancellationIT#will_cache_invalid_cql

The test method `will_cache_invalid_cql` is inherently flaky due to the
usage of weak valued cache. This is a quick workaround that should
achieve the same end result as the setup in PreparedStatementCachingIT.
Here we use reflection to forcibly change the cache used by the
request processor.

The alternatives are: reimplementing similar setup as in
PreparedStatementCachingIT with some changes. That means
having a test version of DefaultDriverContext, CqlPrepareAsyncProcessor,
SessionBuilder and necessary methods.

The other option is moving this test method to the PreparedStatementCachingIT,
but then the cache's remove callback which is used there needs to be adjusted,
otherwise the test will still be flaky, but with different cause. The
server-side error about invalid syntax can occasionally break the remove
callback.

Author: Bouncheck

integration-tests/src/test/java/com/datastax/oss/driver/core/cql/PreparedStatementCancellationIT.java

@@ -31,7 +31,9 @@
 import com.datastax.oss.driver.internal.core.cql.CqlPrepareAsyncProcessor;
 import com.datastax.oss.driver.shaded.guava.common.base.Predicates;
 import com.datastax.oss.driver.shaded.guava.common.cache.Cache;
+import com.datastax.oss.driver.shaded.guava.common.cache.CacheBuilder;
 import com.datastax.oss.driver.shaded.guava.common.collect.Iterables;
+import java.lang.reflect.Field;
 import java.util.concurrent.CompletableFuture;
 import org.junit.After;
 import org.junit.Before;
@@ -118,6 +120,15 @@ public void will_cache_invalid_cql() throws Exception {
 
     CqlSession session = SessionUtils.newSession(ccmRule, sessionRule.keyspace());
     CqlPrepareAsyncProcessor processor = findProcessor(session);
+
+    // Forcibly replace the cache with strong-valued one to make sure this test does not fail due to
+    // GC
+    Field cacheField = CqlPrepareAsyncProcessor.class.getDeclaredField("cache");
+    cacheField.setAccessible(true);
+    Cache<PrepareRequest, CompletableFuture<PreparedStatement>> newCache =
+        CacheBuilder.newBuilder().build();
+    cacheField.set(processor, newCache);
+
     Cache<PrepareRequest, CompletableFuture<PreparedStatement>> cache = processor.getCache();
     assertThat(cache.size()).isEqualTo(0);