Add test case for txn try

test/try.cc

@@ -0,0 +1,38 @@
+#include "test.h"
+
+bool testcase_try::setup() {
+  log_trace(">> setup");
+  if (!inherited::setup())
+    return false;
+
+  log_trace("<< setup");
+  return true;
+}
+
+bool testcase_try::run() {
+  db_open();
+  assert(!txn_guard);
+
+  MDBX_txn *txn = nullptr;
+  MDBX_txn *txn2 = nullptr;
+  int rc =
+      mdbx_txn_begin(db_guard.get(), nullptr, 0, &txn);
+  if (unlikely(rc != MDBX_SUCCESS))
+    failure_perror("mdbx_txn_begin(MDBX_TRYTXN)", rc);
+  else {
+    rc = mdbx_txn_begin(db_guard.get(), nullptr, MDBX_TRYTXN, &txn2);
+    if (unlikely(rc != MDBX_BUSY))
+      failure_perror("mdbx_txn_begin(MDBX_TRYTXN)", rc);
+  }
+
+  txn_guard.reset(txn);
+  return true;
+}
+
+bool testcase_try::teardown() {
+  log_trace(">> teardown");
+  cursor_guard.release();
+  txn_guard.release();
+  db_guard.release();
+  return inherited::teardown();
+}