test: cover newly-stabilized logout, MCP-over-ACP, and Error edge cases

[cursor]

Risky behavior now covered

Three areas that recently changed or had thin coverage and would silently regress on the wire if anything shifted:

• Logout method (just stabilized in feat: Stabilize logout method agentclientprotocol/agent-client-protocol#1273) had zero unit tests after losing its #[cfg(feature = "unstable_logout")] gates. Wire-format pinning, _meta round-tripping, AGENT_METHOD_NAMES.logout/ClientRequest::method() linkage, default-on-error tolerance on AgentAuthCapabilities::logout, and threading through AgentCapabilities.auth.
• MCP-over-ACP (recent feature feat(unstable): Add experimental MCP-over-ACP message types agentclientprotocol/agent-client-protocol#1185) only had one method-name smoke test in agent.rs. The actual mcp.rs types (ConnectMcp{Request,Response}, MessageMcp{Request,Notification,Response}, DisconnectMcp{Request,Response}) had no serialization tests. Particularly important: the docs-stated invariant that omitted params and explicit null params MUST both decode to None, and that MessageMcpResponse (a transparent Arc<RawValue> wrapper) forwards inner MCP results verbatim.
• Error had only ErrorCode numeric round-trip coverage. The Display impl (empty-message fallback, pretty-printed data suffix), From<serde_json::Error> (InvalidParams + message in data), From<anyhow::Error> downcast behavior (the bug-prone branch that must preserve an inner ACP Error instead of re-wrapping it as InternalError), into_internal_error, and resource_not_found(uri) with/without URI were all untested.

Test files added/updated

• src/v1/error.rs — 11 new tests for Error::Display, conversions, constructors, and resource_not_found URI attachment.
• src/v1/agent.rs — 7 new tests for the stabilized logout method, LogoutRequest/Response/Capabilities, and AgentAuthCapabilities (including the malformed-field tolerance behavior baked in by DefaultOnError).
• src/v1/mcp.rs — new tests module with 11 tests pinning the MCP-over-ACP wire format end-to-end.
• src/v2/{error,agent,mcp}.rs — mirrored tests in the v2 scaffold so the parallel module can't drift silently.

Net: +60 tests (268 → 328 with --all-features; 41 → 60 default features). cargo test --lib, cargo test --lib --all-features, cargo clippy --all-features, and cargo fmt --check all pass.

Why these tests materially reduce regression risk

• Logout is freshly stabilized. Stabilization PRs that move code out from under #[cfg] flags often silently lose test coverage; pinning the wire name ("logout"), the {} request/response shape, the _meta round-trip, the "supplying {} means supported" capability convention, and the DefaultOnError tolerance closes that gap before any client integrates against it.
• MCP-over-ACP is brand new and feature-flagged. Any change to field naming (camelCase via serde), omission semantics (skip_serializing_none + Option<Map>), or method-name constants (mcp/connect, mcp/message, mcp/disconnect) would silently break every IDE/agent pair. The "omitted vs explicit null params" test specifically guards a documented invariant that's easy to lose during refactors.
• Error conversions are infrastructure for every method. The anyhow::Error downcast in particular is the kind of subtle code that's easy to "fix" into re-wrapping behavior; the new test makes that an immediate failure. The Display impl handles two formatting branches (empty message, data suffix) that could regress to a bare numeric string or panic on data formatting.

All tests are deterministic, self-contained (serde_json only, no I/O, no concurrency), and run in the existing cargo test --lib pipeline.

  

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Summary by cubic

Add tests to pin the wire format and behavior for the stabilized logout method, MCP-over-ACP connect/message/disconnect, and Error conversions/formatting across v1 and v2. Tests only; no runtime changes.

• New Tests
  • Logout: method name "logout", {} request/response, _meta round-trip, capability advertising via {}, and DefaultOnError tolerance in AgentAuthCapabilities/AgentCapabilities.
  • MCP-over-ACP: method constants ("mcp/connect", "mcp/message", "mcp/disconnect"); ConnectMcp*/MessageMcp*/DisconnectMcp* serialization; omitted vs null params both decode to None; MessageMcpResponse forwards inner JSON verbatim; _meta round-trip.
  • Error: Display (empty message falls back to code; pretty data suffix); From<serde_json::Error> → InvalidParams with message in data; From<anyhow::Error> preserves inner ACP Error else InternalError; into_internal_error; resource_not_found with/without URI; numeric code and JSON-RPC object shape pinned.

^{Written for commit 6adb0fe. Summary will update on new commits.}

Note

Add tests covering logout, MCP-over-ACP, and Error wire behavior for v1 and v2

• Adds serialization round-trip tests for logout (LogoutRequest/LogoutResponse) and AgentAuthCapabilities in both src/v1/agent.rs and src/v2/agent.rs, including DefaultOnError tolerance for malformed logout values.
• Pins MCP-over-ACP wire surface in src/v1/mcp.rs and src/v2/mcp.rs: method name constants, connect/disconnect round-trips, message params omission when unset, null decoding, and verbatim RawValue preservation.
• Covers ErrorCode and Error behaviors in src/v1/error.rs and src/v2/error.rs: numeric conversions, constructor codes, Display output, From<serde_json::Error> and From<anyhow::Error> mappings, and JSON-RPC object serialization shape.

^{Macroscope summarized 6adb0fe.}