fix: Introduce retry for transient errors from DB (#3167)

tests/unit/data/cassandra/ErrorTests.cpp

@@ -0,0 +1,43 @@
+#include "data/cassandra/Error.hpp"
+
+#include <cassandra.h>
+#include <gtest/gtest.h>
+
+#include <cstdint>
+
+using namespace data::cassandra;
+
+namespace {
+
+CassandraError
+makeError(uint32_t const code)
+{
+    return CassandraError{"some error", code};
+}
+
+}  // namespace
+
+// isInvalidQuery is load bearing: DefaultExecutionStrategy::throwErrorIfNeeded treats it as the
+// only permanent failure and retries everything else, so anything wrongly reported here would be
+// retried forever (if false) or surfaced as a fatal std::runtime_error (if true).
+TEST(BackendCassandraErrorTest, IsInvalidQueryOnlyForInvalidQuery)
+{
+    EXPECT_TRUE(makeError(CASS_ERROR_SERVER_INVALID_QUERY).isInvalidQuery());
+
+    EXPECT_FALSE(makeError(CASS_ERROR_SERVER_READ_FAILURE).isInvalidQuery());
+    EXPECT_FALSE(makeError(CASS_ERROR_SERVER_WRITE_FAILURE).isInvalidQuery());
+    EXPECT_FALSE(makeError(CASS_ERROR_SERVER_READ_TIMEOUT).isInvalidQuery());
+    EXPECT_FALSE(makeError(CASS_ERROR_SERVER_UNAVAILABLE).isInvalidQuery());
+    EXPECT_FALSE(makeError(CASS_ERROR_SERVER_SYNTAX_ERROR).isInvalidQuery());
+    EXPECT_FALSE(makeError(CASS_OK).isInvalidQuery());
+}
+
+TEST(BackendCassandraErrorTest, MessageAndCodeArePreserved)
+{
+    // throwErrorIfNeeded puts message() into the DatabaseError it throws, so that treating an
+    // unclassified error as a timeout still reports what actually failed
+    auto const err = CassandraError{"received 1 responses and 1 failures", 0x1300};
+
+    EXPECT_EQ(err.message(), "received 1 responses and 1 failures");
+    EXPECT_EQ(err.code(), 0x1300u);
+}