test: add unit test for the private broadcast storage

diff --git a/src/test/CMakeLists.txt b/src/test/CMakeLists.txt
index 83cb989a..e70eaf5c 100644
--- a/src/test/CMakeLists.txt
+++ b/src/test/CMakeLists.txt
@@ -76,6 +76,7 @@ add_executable(test_bitcoin
   pool_tests.cpp
   pow_tests.cpp
   prevector_tests.cpp
+  private_broadcast_tests.cpp
   raii_event_tests.cpp
   random_tests.cpp
   rbf_tests.cpp
diff --git a/src/test/private_broadcast_tests.cpp b/src/test/private_broadcast_tests.cpp
new file mode 100644
index 00000000..6c5ef36f
--- /dev/null
+++ b/src/test/private_broadcast_tests.cpp
@@ -0,0 +1,96 @@
+// Copyright (c) 2025-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <primitives/transaction.h>
+#include <private_broadcast.h>
+#include <test/util/setup_common.h>
+#include <util/time.h>
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(private_broadcast_tests, BasicTestingSetup)
+
+static CTransactionRef MakeDummyTx(uint32_t id, size_t num_witness)
+{
+    CMutableTransaction mtx;
+    mtx.vin.resize(1);
+    mtx.vin[0].nSequence = id;
+    if (num_witness > 0) {
+        mtx.vin[0].scriptWitness = CScriptWitness{};
+        mtx.vin[0].scriptWitness.stack.resize(num_witness);
+    }
+    return MakeTransactionRef(mtx);
+}
+
+BOOST_AUTO_TEST_CASE(basic)
+{
+    SetMockTime(Now<NodeSeconds>());
+
+    PrivateBroadcast pb;
+    const NodeId recipient1{1};
+
+    // No transactions initially.
+    BOOST_CHECK(!pb.PickTxForSend(/*will_send_to_nodeid=*/recipient1).has_value());
+    BOOST_CHECK_EQUAL(pb.GetStale().size(), 0);
+    BOOST_CHECK(!pb.HavePendingTransactions());
+
+    // Make a transaction and add it.
+    const auto tx1{MakeDummyTx(/*id=*/1, /*num_witness=*/0)};
+
+    BOOST_CHECK(pb.Add(tx1));
+    BOOST_CHECK(!pb.Add(tx1));
+
+    // Make another transaction with same txid, different wtxid and add it.
+    const auto tx2{MakeDummyTx(/*id=*/1, /*num_witness=*/1)};
+    BOOST_REQUIRE(tx1->GetHash() == tx2->GetHash());
+    BOOST_REQUIRE(tx1->GetWitnessHash() != tx2->GetWitnessHash());
+
+    BOOST_CHECK(pb.Add(tx2));
+
+    const auto tx_for_recipient1{pb.PickTxForSend(/*will_send_to_nodeid=*/recipient1).value()};
+    BOOST_CHECK(tx_for_recipient1 == tx1 || tx_for_recipient1 == tx2);
+
+    // A second pick must return the other transaction.
+    const NodeId recipient2{2};
+    const auto tx_for_recipient2{pb.PickTxForSend(/*will_send_to_nodeid=*/recipient2).value()};
+    BOOST_CHECK(tx_for_recipient2 == tx1 || tx_for_recipient2 == tx2);
+    BOOST_CHECK_NE(tx_for_recipient1, tx_for_recipient2);
+
+    const NodeId nonexistent_recipient{0};
+
+    // Confirm transactions <-> recipients mapping is correct.
+    BOOST_CHECK(!pb.GetTxForNode(nonexistent_recipient).has_value());
+    BOOST_CHECK_EQUAL(pb.GetTxForNode(recipient1).value(), tx_for_recipient1);
+    BOOST_CHECK_EQUAL(pb.GetTxForNode(recipient2).value(), tx_for_recipient2);
+
+    // Confirm none of the transactions' reception have been confirmed.
+    BOOST_CHECK(!pb.DidNodeConfirmReception(recipient1));
+    BOOST_CHECK(!pb.DidNodeConfirmReception(recipient2));
+    BOOST_CHECK(!pb.DidNodeConfirmReception(nonexistent_recipient));
+
+    BOOST_CHECK_EQUAL(pb.GetStale().size(), 2);
+
+    // Confirm reception by recipient1.
+    pb.NodeConfirmedReception(nonexistent_recipient); // Dummy call.
+    pb.NodeConfirmedReception(recipient1);
+
+    BOOST_CHECK(pb.DidNodeConfirmReception(recipient1));
+    BOOST_CHECK(!pb.DidNodeConfirmReception(recipient2));
+
+    BOOST_CHECK_EQUAL(pb.GetStale().size(), 1);
+    BOOST_CHECK_EQUAL(pb.GetStale()[0], tx_for_recipient2);
+
+    SetMockTime(Now<NodeSeconds>() + 10h);
+
+    BOOST_CHECK_EQUAL(pb.GetStale().size(), 2);
+
+    BOOST_CHECK_EQUAL(pb.Remove(tx_for_recipient1).value(), 1);
+    BOOST_CHECK(!pb.Remove(tx_for_recipient1).has_value());
+    BOOST_CHECK_EQUAL(pb.Remove(tx_for_recipient2).value(), 0);
+    BOOST_CHECK(!pb.Remove(tx_for_recipient2).has_value());
+
+    BOOST_CHECK(!pb.PickTxForSend(/*will_send_to_nodeid=*/nonexistent_recipient).has_value());
+}
+
+BOOST_AUTO_TEST_SUITE_END()