Introduce MockableDatabase for wallet unit tests

MockableDatabase is a WalletDatabase that allows us to interact with the
records to change them independently from the wallet, as well as
changing the return values from within the tests. This will give us
greater flexibility in testing the wallet.

src/wallet/test/util.h

@@ -6,6 +6,8 @@
 #define BITCOIN_WALLET_TEST_UTIL_H
 
 #include <script/standard.h>
+#include <wallet/db.h>
+
 #include <memory>
 
 class ArgsManager;
@@ -31,6 +33,78 @@ std::string getnewaddress(CWallet& w);
 /** Returns a new destination, of an specific type, from the wallet */
 CTxDestination getNewDestination(CWallet& w, OutputType output_type);
 
+class MockableCursor: public DatabaseCursor
+{
+public:
+    std::map<SerializeData, SerializeData>::const_iterator m_cursor;
+    std::map<SerializeData, SerializeData>::const_iterator m_cursor_end;
+    bool m_pass;
+
+    explicit MockableCursor(const std::map<SerializeData, SerializeData>& records, bool pass) : m_cursor(records.begin()), m_cursor_end(records.end()), m_pass(pass) {}
+    ~MockableCursor() {}
+
+    Status Next(DataStream& key, DataStream& value) override;
+};
+
+class MockableBatch : public DatabaseBatch
+{
+private:
+    std::map<SerializeData, SerializeData>& m_records;
+    bool m_pass;
+
+    bool ReadKey(DataStream&& key, DataStream& value) override;
+    bool WriteKey(DataStream&& key, DataStream&& value, bool overwrite=true) override;
+    bool EraseKey(DataStream&& key) override;
+    bool HasKey(DataStream&& key) override;
+    bool ErasePrefix(Span<const std::byte> prefix) override;
+
+public:
+    explicit MockableBatch(std::map<SerializeData, SerializeData>& records, bool pass) : m_records(records), m_pass(pass) {}
+    ~MockableBatch() {}
+
+    void Flush() override {}
+    void Close() override {}
+
+    std::unique_ptr<DatabaseCursor> GetNewCursor() override
+    {
+        return std::make_unique<MockableCursor>(m_records, m_pass);
+    }
+    bool TxnBegin() override { return m_pass; }
+    bool TxnCommit() override { return m_pass; }
+    bool TxnAbort() override { return m_pass; }
+};
+
+/** A WalletDatabase whose contents and return values can be modified as needed for testing
+ **/
+class MockableDatabase : public WalletDatabase
+{
+public:
+    std::map<SerializeData, SerializeData> m_records;
+    bool m_pass{true};
+
+    MockableDatabase(std::map<SerializeData, SerializeData> records = {}) : WalletDatabase(), m_records(records) {}
+    ~MockableDatabase() {};
+
+    void Open() override {}
+    void AddRef() override {}
+    void RemoveRef() override {}
+
+    bool Rewrite(const char* pszSkip=nullptr) override { return m_pass; }
+    bool Backup(const std::string& strDest) const override { return m_pass; }
+    void Flush() override {}
+    void Close() override {}
+    bool PeriodicFlush() override { return m_pass; }
+    void IncrementUpdateCounter() override {}
+    void ReloadDbEnv() override {}
+
+    std::string Filename() override { return "mockable"; }
+    std::string Format() override { return "mock"; }
+    std::unique_ptr<DatabaseBatch> MakeBatch(bool flush_on_close = true) override { return std::make_unique<MockableBatch>(m_records, m_pass); }
+};
+
+std::unique_ptr<WalletDatabase> CreateMockableWalletDatabase(std::map<SerializeData, SerializeData> records = {});
+
+MockableDatabase& GetMockableDatabase(CWallet& wallet);
 } // namespace wallet
 
 #endif // BITCOIN_WALLET_TEST_UTIL_H