diff --git a/tests/unit_tests/prepare_outputs_entries_for_key_offsets.cpp b/tests/unit_tests/prepare_outputs_entries_for_key_offsets.cpp
new file mode 100644
index 00000000..d8baa9b6
--- /dev/null
+++ b/tests/unit_tests/prepare_outputs_entries_for_key_offsets.cpp
@@ -0,0 +1,139 @@
+#include "gtest/gtest.h"
+#include "currency_core/currency_format_utils_abstract.h"
+#include "currency_core/currency_format_utils_transactions.h"
+
+TEST(prepare_outputs_for_key_offsets, size_lower_than_2)
+{
+  for (size_t size{}; size < 2; ++size)
+  {
+    std::vector<currency::tx_source_entry::output_entry> outputs(size);
+    size_t index{SIZE_MAX};
+
+    ASSERT_EQ(currency::prepare_outputs_entries_for_key_offsets(outputs, 0, index), outputs);
+    ASSERT_EQ(index, 0);
+  }
+}
+
+TEST(prepare_outputs_for_key_offsets, pass_index_greater_or_equal_to_length_of_outputs_container)
+{
+  const std::vector<currency::tx_source_entry::output_entry> outputs(2);
+
+  {
+    auto index{crypto::rand<size_t>()};
+    const auto index_before_preparing_outputs{index};
+
+    ASSERT_TRUE(currency::prepare_outputs_entries_for_key_offsets(outputs, outputs.size(), index).empty());
+    ASSERT_EQ(index, index_before_preparing_outputs);
+  }
+
+  {
+    auto index{crypto::rand<size_t>()};
+    const auto index_before_preparing_outputs{index};
+
+    ASSERT_TRUE(currency::prepare_outputs_entries_for_key_offsets(outputs, outputs.size() + 1, index).empty());
+    ASSERT_EQ(index, index_before_preparing_outputs);
+  }
+
+  {
+    auto index{crypto::rand<size_t>()};
+    const auto index_before_preparing_outputs{index};
+
+    ASSERT_TRUE(currency::prepare_outputs_entries_for_key_offsets(outputs, SIZE_MAX - 1, index).empty());
+    ASSERT_EQ(index, index_before_preparing_outputs);
+  }
+
+  {
+    auto index{crypto::rand<size_t>()};
+    const auto index_before_preparing_outputs{index};
+
+    ASSERT_EQ(currency::prepare_outputs_entries_for_key_offsets(outputs, SIZE_MAX, index), outputs);
+    ASSERT_EQ(index, index_before_preparing_outputs);
+  }
+}
+
+TEST(prepare_outputs_for_key_offsets, uint64_reference_lower_than_by_id_reference)
+{
+  std::vector<currency::tx_source_entry::output_entry> outputs{}, expected_prepared_outputs{};
+  size_t index{};
+
+  outputs.reserve(2);
+  outputs.emplace_back(currency::ref_by_id{}, currency::null_pkey);
+  outputs.emplace_back(0, currency::null_pkey);
+  expected_prepared_outputs.reserve(outputs.size());
+  expected_prepared_outputs.emplace_back(0, currency::null_pkey);
+  expected_prepared_outputs.emplace_back(currency::ref_by_id{}, currency::null_pkey);
+  ASSERT_EQ(outputs.size(), expected_prepared_outputs.size());
+  ASSERT_EQ(currency::prepare_outputs_entries_for_key_offsets(outputs, 0, index), expected_prepared_outputs);
+  ASSERT_EQ(index, 1);
+}
+
+TEST(prepare_outputs_for_key_offsets, subsequence_of_ref_by_id_references_is_not_changed)
+{
+  {
+    std::vector<currency::tx_source_entry::output_entry> outputs{}, expected_prepared_outputs{};
+    size_t index{};
+
+    outputs.reserve(6);
+    outputs.emplace_back(3, currency::null_pkey);
+    outputs.emplace_back(currency::ref_by_id{currency::null_hash, 1}, currency::null_pkey);
+    outputs.emplace_back(currency::ref_by_id{currency::null_hash, 0}, currency::null_pkey);
+    outputs.emplace_back(2, currency::null_pkey);
+    outputs.emplace_back(currency::ref_by_id{currency::null_hash, 3}, currency::null_pkey);
+    outputs.emplace_back(1, currency::null_pkey);
+    expected_prepared_outputs.reserve(outputs.size());
+    expected_prepared_outputs.emplace_back(1, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(1, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(1, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 1}, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 0}, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 3}, currency::null_pkey);
+    ASSERT_EQ(outputs.size(), expected_prepared_outputs.size());
+    ASSERT_EQ(currency::prepare_outputs_entries_for_key_offsets(outputs, 0, index), expected_prepared_outputs);
+    ASSERT_EQ(index, 2);
+  }
+
+  {
+    std::vector<currency::tx_source_entry::output_entry> outputs{}, expected_prepared_outputs{};
+    size_t index{};
+
+    outputs.reserve(5);
+    outputs.emplace_back(currency::ref_by_id{currency::null_hash, 1}, currency::null_pkey);
+    outputs.emplace_back(currency::ref_by_id{currency::null_hash, 0}, currency::null_pkey);
+    outputs.emplace_back(currency::ref_by_id{currency::null_hash, 3}, currency::null_pkey);
+    outputs.emplace_back(1, currency::null_pkey);
+    outputs.emplace_back(0, currency::null_pkey);
+    expected_prepared_outputs.reserve(outputs.size());
+    expected_prepared_outputs.emplace_back(0, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(1, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 1}, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 0}, currency::null_pkey);
+    expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 3}, currency::null_pkey);
+    ASSERT_EQ(outputs.size(), expected_prepared_outputs.size());
+    ASSERT_EQ(currency::prepare_outputs_entries_for_key_offsets(outputs, 0, index), expected_prepared_outputs);
+    ASSERT_EQ(outputs.at(0), expected_prepared_outputs.at(2));
+    ASSERT_EQ(index, 2);
+  }
+}
+
+TEST(prepare_outputs_for_key_offsets, index_will_not_be_changed_if_old_index_is_size_max)
+{
+  std::vector<currency::tx_source_entry::output_entry> outputs{}, expected_prepared_outputs{};
+  auto index{crypto::rand<size_t>()};
+  const auto index_before_preparing_outputs{index};
+
+  outputs.reserve(5);
+  outputs.emplace_back(currency::ref_by_id{currency::null_hash, 1}, currency::null_pkey);
+  outputs.emplace_back(currency::ref_by_id{currency::null_hash, 0}, currency::null_pkey);
+  outputs.emplace_back(currency::ref_by_id{currency::null_hash, 3}, currency::null_pkey);
+  outputs.emplace_back(1, currency::null_pkey);
+  outputs.emplace_back(0, currency::null_pkey);
+  expected_prepared_outputs.reserve(outputs.size());
+  expected_prepared_outputs.emplace_back(0, currency::null_pkey);
+  expected_prepared_outputs.emplace_back(1, currency::null_pkey);
+  expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 1}, currency::null_pkey);
+  expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 0}, currency::null_pkey);
+  expected_prepared_outputs.emplace_back(currency::ref_by_id{currency::null_hash, 3}, currency::null_pkey);
+  ASSERT_EQ(outputs.size(), expected_prepared_outputs.size());
+  ASSERT_EQ(currency::prepare_outputs_entries_for_key_offsets(outputs, SIZE_MAX, index), expected_prepared_outputs);
+  ASSERT_EQ(index, index_before_preparing_outputs);
+}