test: improve coverage for discovery v5 UDP transport (71%)

[tcoratger]

Summary

src/lean_spec/subspecs/networking/discovery/transport.py has 71% test coverage. While test_transport.py exists, many packet handling paths, the multi-response FINDNODE flow, and response sending are not covered.

Coverage stats:

File	Statements	Covered	Coverage
discovery/transport.py	299	72 uncovered	71%

Uncovered lines: 313, 349–350, 413, 417–430 (FINDNODE multi-response collection), 468, 547 (dummy key handshake trigger), 589–594 (connect flow), 621–699 (WHOAREYOU response handling), 714–737 (handshake response handling), 763–777 (message decryption failure → WHOAREYOU), 889–903 (send_response)

What needs testing

DiscoveryTransport — Request/response

send_ping()

• Happy path: Sends PING, receives PONG, returns Pong
• Timeout: No response within timeout, returns None
• Non-PONG response: Unexpected message type, returns None

send_findnode()

• Single NODES response: One response with total=1
• Multi-response: Multiple NODES messages collected until total reached
• Timeout during collection: Partial results returned
• Empty results: NODES with empty ENR list

send_talkreq()

• Happy path: Sends TALKREQ, receives TALKRESP
• Timeout: Returns None

send_response()

• Happy path: Encrypts and sends response using existing session
• No session: Returns False
• Transport not started: Returns False

Packet handling

_handle_packet()

• MESSAGE packet: Routes to _handle_message()
• WHOAREYOU packet: Routes to _handle_whoareyou()
• HANDSHAKE packet: Routes to _handle_handshake()
• Decode error: Logged and dropped gracefully

_handle_whoareyou()

• Matching pending request: Finds request by nonce, creates handshake response
• No matching request: Logs debug and returns
• No cached ENR: Cannot complete handshake, returns
• Handshake error: Logged and dropped

_handle_handshake()

• Valid handshake: Completes handshake, decrypts message, dispatches
• Handshake failure: Logged and dropped

_handle_message()

• With session: Decrypts and dispatches message
• No session: Sends WHOAREYOU challenge
• Decryption failure: Sends WHOAREYOU challenge

_handle_decoded_message()

• Pending single request: Resolves future with response
• Pending multi request: Queues to response queue
• Unsolicited message: Passed to message handler callback

_build_message_packet()

• With session: Uses session send key for encryption
• Without session: Uses dummy key to trigger handshake

Lifecycle

• start(): Creates UDP endpoint, sets running flag
• stop(): Closes transport, cancels pending requests
• register_node_address() / get_node_address(): Address lookup
• register_enr() / get_enr(): ENR cache delegation

Why this matters

• Discovery reliability: This is how nodes find each other. Bugs here mean network isolation
• Handshake correctness: The deliberate-failure handshake initiation is subtle and must work precisely
• Multi-response handling: FINDNODE's split-response pattern is error-prone without tests

How to test

Running tests with coverage

uv run pytest tests/lean_spec/subspecs/networking/discovery/test_transport.py -v \
  --cov=src/lean_spec/subspecs/networking/discovery/transport --cov-report=term-missing

Target: ≥85% line coverage.

Test file location

tests/lean_spec/subspecs/networking/discovery/test_transport.py  (extend existing)

Testing tips

• Mock asyncio.DatagramTransport for send verification
• Use SessionCache with pre-populated sessions for message handling tests
• Construct PacketHeader and event instances directly for _handle_* methods
• For multi-response tests, use asyncio.Queue to simulate NODES arrivals
• Use the existing conftest.py fixtures in the discovery test directory

Using Claude Code subagents

1. code-tester agent — Generate the tests

Extend tests in tests/lean_spec/subspecs/networking/discovery/test_transport.py. Cover send_findnode multi-response collection, send_response with/without session, _handle_whoareyou with matching/missing pending request, _handle_message with/without session (decryption failure path), _handle_decoded_message routing to single/multi/handler, and _build_message_packet with/without session.

Workflow

1. Start with pure request/response tests (send_ping, send_response)
2. Test packet handling with constructed headers and events
3. Test multi-response FINDNODE collection
4. Test handshake trigger via dummy key
5. Run uvx tox -e all-checks to pass all quality checks

[dicethedev]

I will like to pick this up

[tcoratger]

I will like to pick this up

Assigned

[dicethedev]

@tcoratger I was about to open a PR, but it looks like the issue has already been resolved. All good, I’ll wait for the next one.

For next time @Smartdevs17, it’d be great to follow open source best practices by letting the person an issue is assigned to handle it. Maybe if an issue has been idle for 5 days or more, it could then be picked up by someone else.

[tcoratger]

@tcoratger I was about to open a PR, but it looks like the issue has already been resolved. All good, I’ll wait for the next one.

For next time @Smartdevs17, it’d be great to follow open source best practices by letting the person an issue is assigned to handle it. Maybe if an issue has been idle for 5 days or more, it could then be picked up by someone else.

Yeah sorry for this, will open couple of new ones, I merged the PR since the work was already done but yes I agree let's follow the best practices next time.

[dicethedev]

@tcoratger Thanks for the update! No worries at all. I appreciate you merging the PR since the work was already done.
Let’s keep pushing LeanEthereum, testing it thoroughly, and making it even more secure. Excited for what’s ahead!