test(stf): add unit tests for processDepositRequest

Test coverage for Electra deposit request processing:
- First request sets depositRequestsStartIndex from UNSET
- Subsequent requests preserve existing start index
- Pending deposit fields (amount, slot) match input request
- Already-set start index is not overwritten

🤖 Generated with AI assistance

Author: lodekeeper-z

src/state_transition/block/process_deposit_request.zig

@@ -22,3 +22,121 @@ pub fn processDepositRequest(comptime fork: ForkSeq, state: *BeaconState(fork),
     var pending_deposits = try state.pendingDeposits();
     try pending_deposits.pushValue(&pending_deposit);
 }
+
+// ─── Tests ──────────────────────────────────────────────────────────────────
+
+const std = @import("std");
+const testing = std.testing;
+const Node = @import("persistent_merkle_tree").Node;
+const TestCachedBeaconState = @import("../test_utils/generate_state.zig").TestCachedBeaconState;
+
+fn makeDepositRequest(index: u64) DepositRequest {
+    return DepositRequest{
+        .pubkey = [_]u8{@as(u8, @intCast(index & 0xFF))} ** 48,
+        .withdrawal_credentials = [_]u8{0x01} ++ [_]u8{0} ** 11 ++ [_]u8{0xAA} ** 20,
+        .amount = 32_000_000_000,
+        .signature = [_]u8{0} ** 96,
+        .index = index,
+    };
+}
+
+test "processDepositRequest - first request sets depositRequestsStartIndex" {
+    const allocator = testing.allocator;
+    var pool = try Node.Pool.init(allocator, 256 * 5);
+    defer pool.deinit();
+
+    var test_state = try TestCachedBeaconState.init(allocator, &pool, 16);
+    defer test_state.deinit();
+
+    var state = test_state.cached_state.state.castToFork(.electra);
+
+    // Set to UNSET value (as electra upgrade does)
+    try state.setDepositRequestsStartIndex(c.UNSET_DEPOSIT_REQUESTS_START_INDEX);
+
+    const request = makeDepositRequest(42);
+    try processDepositRequest(.electra, state, &request);
+
+    // Should have set the start index to the request's index
+    try testing.expectEqual(@as(u64, 42), try state.depositRequestsStartIndex());
+
+    // Should have appended one pending deposit
+    var pending = try state.pendingDeposits();
+    try testing.expectEqual(@as(u64, 1), try pending.length());
+}
+
+test "processDepositRequest - subsequent request does not change start index" {
+    const allocator = testing.allocator;
+    var pool = try Node.Pool.init(allocator, 256 * 5);
+    defer pool.deinit();
+
+    var test_state = try TestCachedBeaconState.init(allocator, &pool, 16);
+    defer test_state.deinit();
+
+    var state = test_state.cached_state.state.castToFork(.electra);
+
+    // Set to UNSET, then process first request
+    try state.setDepositRequestsStartIndex(c.UNSET_DEPOSIT_REQUESTS_START_INDEX);
+    const first = makeDepositRequest(10);
+    try processDepositRequest(.electra, state, &first);
+
+    // Process second request with different index
+    const second = makeDepositRequest(20);
+    try processDepositRequest(.electra, state, &second);
+
+    // Start index should still be 10 (from first request)
+    try testing.expectEqual(@as(u64, 10), try state.depositRequestsStartIndex());
+
+    // Should have two pending deposits
+    var pending = try state.pendingDeposits();
+    try testing.expectEqual(@as(u64, 2), try pending.length());
+}
+
+test "processDepositRequest - pending deposit fields match request" {
+    const allocator = testing.allocator;
+    var pool = try Node.Pool.init(allocator, 256 * 5);
+    defer pool.deinit();
+
+    var test_state = try TestCachedBeaconState.init(allocator, &pool, 16);
+    defer test_state.deinit();
+
+    var state = test_state.cached_state.state.castToFork(.electra);
+
+    // Use a non-UNSET start index so we skip that branch
+    try state.setDepositRequestsStartIndex(0);
+
+    const request = makeDepositRequest(5);
+    try processDepositRequest(.electra, state, &request);
+
+    var pending = try state.pendingDeposits();
+    var deposit = try pending.get(0);
+
+    // Verify all fields were copied correctly
+    // Verify amount and slot were correctly copied from the request
+
+    const amount_view = try deposit.get("amount");
+    try testing.expectEqual(@as(u64, 32_000_000_000), amount_view);
+
+    const slot_view = try deposit.get("slot");
+    const state_slot = try state.slot();
+    try testing.expectEqual(state_slot, slot_view);
+}
+
+test "processDepositRequest - already set start index is preserved" {
+    const allocator = testing.allocator;
+    var pool = try Node.Pool.init(allocator, 256 * 5);
+    defer pool.deinit();
+
+    var test_state = try TestCachedBeaconState.init(allocator, &pool, 16);
+    defer test_state.deinit();
+
+    var state = test_state.cached_state.state.castToFork(.electra);
+
+    // Pre-set to a specific value (not UNSET)
+    try state.setDepositRequestsStartIndex(100);
+
+    const request = makeDepositRequest(200);
+    try processDepositRequest(.electra, state, &request);
+
+    // Start index should remain 100
+    try testing.expectEqual(@as(u64, 100), try state.depositRequestsStartIndex());
+}