## Changes
The `Setenv` helper function configures an environment variable and
resets it to its original value when exiting the test scope. It is
incompatible with running tests in parallel because it modifies
process-wide state. The `libs/env` package defines functions to interact
with the environment but records `Setenv` calls on a `context.Context`.
This enables us to override/specialize the environment scoped to a
context.
Pre-requisites for removing the `t.Setenv` calls:
* Make `cmdio.NewIO` accept a context and use it with `libs/env`
* Make all `internal/testcli` functions use a context
The rest of this change:
* Modifies integration tests to initialize a context to use if there
wasn't already one
* Updates `t.Setenv` calls to use `env.Set`
## Tests
n/a
## Changes
The CLI test runner instantiates a new CLI "instance" through
`cmd.New()` and runs it with specified arguments. This is as close as we
get to running the real CLI **in-process**. This runner was located in
the `internal` package next to other helpers. This change moves it to
its own dedicated package.
Note: this runner transitively imports pretty much the entire
repository, which is why we intentionally keep it _separate_ from
`testutil`.
## Tests
n/a
Pieter Noordhuis