diff --git a/src/libstore-tests/find-cycles.cc b/src/libstore-tests/find-cycles.cc
new file mode 100644
index 000000000..dbcf9d0a3
--- /dev/null
+++ b/src/libstore-tests/find-cycles.cc
@@ -0,0 +1,146 @@
+#include "nix/store/build/find-cycles.hh"
+
+#include <gtest/gtest.h>
+#include <algorithm>
+
+namespace nix {
+
+/**
+ * Parameters for transformEdgesToMultiedges tests
+ */
+struct TransformEdgesParams
+{
+    std::string description;
+    std::vector<std::vector<std::string>> inputEdges;
+    std::vector<std::vector<std::string>> expectedOutput;
+
+    friend std::ostream & operator<<(std::ostream & os, const TransformEdgesParams & params)
+    {
+        os << "Test: " << params.description << "\n";
+        os << "Input edges (" << params.inputEdges.size() << "):\n";
+        for (const auto & edge : params.inputEdges) {
+            os << "  ";
+            for (size_t i = 0; i < edge.size(); ++i) {
+                if (i > 0)
+                    os << " -> ";
+                os << edge[i];
+            }
+            os << "\n";
+        }
+        os << "Expected output (" << params.expectedOutput.size() << "):\n";
+        for (const auto & multiedge : params.expectedOutput) {
+            os << "  ";
+            for (size_t i = 0; i < multiedge.size(); ++i) {
+                if (i > 0)
+                    os << " -> ";
+                os << multiedge[i];
+            }
+            os << "\n";
+        }
+        return os;
+    }
+};
+
+class TransformEdgesToMultiedgesTest : public ::testing::TestWithParam<TransformEdgesParams>
+{};
+
+namespace {
+// Helper to convert vector<vector<string>> to StoreCycleEdgeVec
+StoreCycleEdgeVec toStoreCycleEdgeVec(const std::vector<std::vector<std::string>> & edges)
+{
+    StoreCycleEdgeVec result;
+    result.reserve(edges.size());
+    for (const auto & edge : edges) {
+        result.emplace_back(edge.begin(), edge.end());
+    }
+    return result;
+}
+
+// Comparator for sorting multiedges deterministically
+bool compareMultiedges(const StoreCycleEdge & a, const StoreCycleEdge & b)
+{
+    if (a.size() != b.size())
+        return a.size() < b.size();
+    return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
+}
+} // namespace
+
+TEST_P(TransformEdgesToMultiedgesTest, TransformEdges)
+{
+    const auto & params = GetParam();
+
+    auto inputEdges = toStoreCycleEdgeVec(params.inputEdges);
+    StoreCycleEdgeVec actualOutput;
+    transformEdgesToMultiedges(inputEdges, actualOutput);
+
+    auto expectedOutput = toStoreCycleEdgeVec(params.expectedOutput);
+
+    ASSERT_EQ(actualOutput.size(), expectedOutput.size()) << "Number of multiedges doesn't match expected";
+
+    // Sort both for comparison (order may vary, but content should match)
+    std::sort(actualOutput.begin(), actualOutput.end(), compareMultiedges);
+    std::sort(expectedOutput.begin(), expectedOutput.end(), compareMultiedges);
+
+    // Compare each multiedge
+    EXPECT_EQ(actualOutput, expectedOutput);
+}
+
+INSTANTIATE_TEST_CASE_P(
+    FindCycles,
+    TransformEdgesToMultiedgesTest,
+    ::testing::Values(
+        // Empty input
+        TransformEdgesParams{"empty input", {}, {}},
+
+        // Single edge - no joining possible
+        TransformEdgesParams{"single edge", {{"a", "b"}}, {{"a", "b"}}},
+
+        // Two edges that connect (append case: A->B, B->C becomes A->B->C)
+        TransformEdgesParams{"two edges connecting via append", {{"a", "b"}, {"b", "c"}}, {{"a", "b", "c"}}},
+
+        // Two edges that connect (prepend case: B->C, A->B becomes A->B->C)
+        TransformEdgesParams{"two edges connecting via prepend", {{"b", "c"}, {"a", "b"}}, {{"a", "b", "c"}}},
+
+        // Complete cycle (A->B, B->C, C->A becomes A->B->C->A)
+        TransformEdgesParams{"complete cycle", {{"a", "b"}, {"b", "c"}, {"c", "a"}}, {{"a", "b", "c", "a"}}},
+
+        // Two disjoint edges - no joining
+        TransformEdgesParams{"disjoint edges", {{"a", "b"}, {"c", "d"}}, {{"a", "b"}, {"c", "d"}}},
+
+        // Chain of multiple edges (A->B, B->C, C->D, D->E)
+        TransformEdgesParams{
+            "chain of edges", {{"a", "b"}, {"b", "c"}, {"c", "d"}, {"d", "e"}}, {{"a", "b", "c", "d", "e"}}},
+
+        // Multiple disjoint cycles
+        TransformEdgesParams{
+            "multiple disjoint cycles",
+            {{"a", "b"}, {"b", "a"}, {"c", "d"}, {"d", "c"}},
+            {{"a", "b", "a"}, {"c", "d", "c"}}},
+
+        // Complex graph requiring multiple merge passes
+        // First pass: (A->B, B->C) -> (A->B->C)
+        // Then: (A->B->C, C->D) -> (A->B->C->D)
+        // Then: (D->A, A->B->C->D) -> (A->B->C->D->A)
+        TransformEdgesParams{
+            "complex requiring multiple passes",
+            {{"a", "b"}, {"b", "c"}, {"c", "d"}, {"d", "a"}},
+            {{"a", "b", "c", "d", "a"}}},
+
+        // Y-shaped graph (A->B, B->C, B->D)
+        // B->C and B->D can't connect, but A->B can prepend to B->C and A->B can prepend to B->D
+        // However, once A->B joins with B->C to form A->B->C, the original A->B is consumed
+        // So we should get A->B->C and B->D (or A->B->D and B->C depending on order)
+        TransformEdgesParams{"Y-shaped graph", {{"a", "b"}, {"b", "c"}, {"b", "d"}}, {{"a", "b", "c"}, {"b", "d"}}},
+
+        // Edge with longer path (multi-hop edge)
+        TransformEdgesParams{
+            "edge with multiple hops", {{"a", "x", "y", "b"}, {"b", "c"}}, {{"a", "x", "y", "b", "c"}}},
+
+        // Self-loop edge
+        TransformEdgesParams{"self-loop", {{"a", "a"}}, {{"a", "a"}}},
+
+        // Reverse order joining (tests prepend logic thoroughly)
+        TransformEdgesParams{
+            "reverse order joining", {{"d", "e"}, {"c", "d"}, {"b", "c"}, {"a", "b"}}, {{"a", "b", "c", "d", "e"}}}));
+
+} // namespace nix
diff --git a/src/libstore-tests/meson.build b/src/libstore-tests/meson.build
index 4d464ad89..7c96fa6b3 100644
--- a/src/libstore-tests/meson.build
+++ b/src/libstore-tests/meson.build
@@ -61,6 +61,7 @@ sources = files(
   'derived-path.cc',
   'downstream-placeholder.cc',
   'dummy-store.cc',
+  'find-cycles.cc',
   'http-binary-cache-store.cc',
   'legacy-ssh-store.cc',
   'local-binary-cache-store.cc',