Relayer v0 tests for client update ping pong

[adizere]

Crate

relayer-cli

Summary

We should add tests that integrate the relayer CLI (and relayer) functionality against a MockChain.

Problem

The proposed relayer v0 architecture (soon to be detailed #326, and captured on the relayer logic side by ADR-004) prescribes that the end functionality of v0 should consist of packet relaying over a single channel. This high-level operation entails many intermediary steps (e.g., finishing client, connection and channel lifecycle across the whole stack).

Since packet relaying is such a distant aim, we propose an intermediary goal: supporting a client update ping-pong, i.e., relay MsgUpdateAnyClient among two chains. This goal was first formulated in #216, called "MVP relayer." A mock version of the MVP relayer, which tests crate ibc in isolation (and entirely bypasses crates relayer and relayer-cli) was fixed through https://github.com/informalsystems/ibc-rs/issues/276. Concretely, see the test client_update_ping_pong:

https://github.com/informalsystems/ibc-rs/blob/12cb1d6187e878eee0e40295fe0b804ddef0b846/modules/src/ics18_relayer/utils.rs#L69

Proposal

The present issue proposes to add a test similar to client_update_ping_pong, which not only exercises the ibc crate but also the relayer. The client updates should work for a local chain (not an actual Cosmos chain), consequently this issue depends on #158. Another essential dependency is #376.

We can also imagine adding a CLI command for invoking and testing automatic client updates. But this does not seem very useful at the moment. Such a CLI may need to be a sub-command of the v0 command.

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