test(python/evm): add unit tests for register helpers

[0xAxiom]

Summary

Adds 30 unit tests for python/x402/x402/mechanisms/evm/exact/register.py — the only source file in mechanisms/evm/exact/ without a dedicated unit test module.

The three public helpers (register_exact_evm_client, register_exact_evm_server, register_exact_evm_facilitator) are the canonical entry points users hit when wiring EVM exact schemes into x402Client, x402ResourceServer, and x402Facilitator (and their sync variants), so direct coverage is worthwhile.

What's tested

register_exact_evm_client (13 tests)

• Returns the same client for chaining
• Default registration: eip155:* V2 wildcard + V1 schemes for every entry in V1_NETWORKS
• networks="eip155:8453" (string) registers a single V2 entry; networks=["eip155:8453", "eip155:1", "eip155:137"] registers each
• Explicit networks suppresses the wildcard fallback but does not suppress the V1 fanout
• policies=[...] appends to the client's policy list; omitting policies leaves it untouched
• Registered V2 scheme is ExactEvmClientScheme with _signer is signer; V1 scheme on "base" is ExactEvmSchemeV1 with _signer is signer
• Bare eth_account.LocalAccount is auto-wrapped in EthAccountSigner via _wrap_if_local_account
• Works against x402ClientSync as well as x402Client

register_exact_evm_server (7 tests)

• Returns the same server for chaining
• Default eip155:* wildcard; networks arg as string or list registers exactly those networks
• Registered scheme is ExactEvmServerScheme
• No V1 entries are added (server registration is V2-only)
• Works against x402ResourceServerSync as well as x402ResourceServer

register_exact_evm_facilitator (10 tests)

• Returns the same facilitator for chaining
• networks as string or list registers each V2 network correctly
• V1 registration always covers the full V1_NETWORKS set
• Registered V2 facilitator is ExactEvmScheme (facilitator) with _signer is signer; V1 is ExactEvmSchemeV1 (facilitator) with _signer is signer
• Default config: both deploy_erc4337_with_eip6492 and simulate_in_settle are False on V2 and V1 configs
• Both flags are propagated identically to V2 and V1 configs
• Setting only one flag leaves the other at default
• Works against x402FacilitatorSync as well as x402Facilitator

Test fixture notes

Client tests use a real EthAccountSigner wrapping a fresh eth_account.Account.create() (no network calls). Facilitator tests use a MagicMock signer with an address attribute — sufficient because register_exact_evm_facilitator only stores the signer reference on the scheme; no signer methods are invoked during registration.

Verification

$ uv run pytest tests/unit/mechanisms/evm/test_register.py -v
======================== 30 passed, 1 warning in 1.13s =========================

$ uv run pytest tests/unit/ -q
======================== 841 passed, 1 warning in 2.84s =========================

$ uvx ruff format tests/unit/mechanisms/evm/test_register.py
1 file left unchanged

$ uvx ruff check tests/unit/mechanisms/evm/test_register.py
All checks passed!

Changelog

Added python/x402/changelog.d/register-helpers-unit-tests.doc.md.

Test plan

• All 30 new tests pass
• Full Python unit suite (841 tests) passes — no regressions
• ruff format and ruff check clean
• Commit GPG-signed and DCO Signed-off-by line included

[cb-heimdall]

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