outdated instructions for integration testing

[bernardoaraujor]

I'm trying to build subxt from source so that I can work on a potential contribution.

While trying to compile, I run into:

$ cargo build
...
error: failed to run custom build command for `test-runtime v0.18.1 (/home/bear/develop/subxt/test-runtime)`

Caused by:
  process didn't exit successfully: `/home/bear/develop/subxt/target/debug/build/test-runtime-92f2fc1489822e0a/build-script-build` (exit status: 101)
  --- stderr
  thread 'main' panicked at 'A substrate binary should be installed on your path for testing purposes. See https://github.com/paritytech/subxt/tree/master#integration-testing', test-runtime/build.rs:62:13
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The integration testing instructions also seem outdated, leading into:

$ cargo install --git https://github.com/paritytech/substrate node-cli --tag=polkadot-v0.9.10 --force
    Updating git repository `https://github.com/paritytech/substrate`
error: failed to find tag `polkadot-v0.9.10`

Caused by:
  reference 'refs/remotes/origin/tags/polkadot-v0.9.10' not found; class=Reference (4); code=NotFound (-3)

[jsdw]

Thanks for letting us know! Yep, those docs don't seem to be correct any more.

In general, master on substrate will be fine, so you can just cargo install --git https://github.com/paritytech/substrate node-cli --force. Every now and then, there is a breaking change in Substrate w.r.t subxt, whic his highlighted by our nightly CI runs on Subxt and is normally addressed reasonably prompty.

[jsdw]

This also relates to #351, which would hide the integration tests behind a feature flag so that you wouldn't require a substrate binary on your path in order to run the basic cargo test.

[Xanewok]

#515 and #546 fixed this; the tests are gated now and the Substrate binary installation instructions now mention the master branch