Add initial acceptance test README

acceptance/README.md

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+## Acceptance Tests
+
+The acceptance tests are blackbox* tests that are expected to interact with resources on a real GitHub instance.
+
+*Note: they aren't strictly blackbox because `exec gh` commands delegate to a binary set up by `testscript` that calls into `ghcmd.Main`. However, since our real `func main` is an extremely thin adapter over `ghcmd.Main`, this is reasonable. This tradeoff avoids us building the binary ourselves for the tests, and allows us to get code coverage metrics.
+
+### Running the Acceptance Tests
+
+The acceptance tests currently require three environment variables to be set:
+ * `GH_HOST`
+ * `GH_ACCEPTANCE_ORG`
+ * `GH_TOKEN`
+
+While `GH_HOST` may not strictly be necessary because `gh` can choose a host, it is required to avoid ambiguity and unexpected results depending on the state of `gh`.
+
+The `GH_ACCEPTANCE_ORG` is an organization that the tests can manage resources in.
+
+The `GH_TOKEN` must already have the necessary scopes for each test, and must have permissions to act in the `GH_ACCEPTANCE_ORG`. See [Effective Test Authoring](#effective-test-authoring) for how tests must handle tokens without sufficient scopes.
+
+The acceptance tests have a build constraint of `//go:build acceptance`, this means that `go test ./...` will continue to work without any modifications. The `acceptance` tag must therefore be provided when running `go test`.
+
+A full example invocation can be found below:
+
+```
+GH_HOST=<host> GH_ACCEPTANCE_ORG=<org> GH_TOKEN=<token> test -tags=acceptance ./acceptance
+```
+
+### Effective Test Authoring
+
+This section will likely extend over time.
+
+#### Test Isolation
+
+#### Scope Validation
+
+#### Limit Custom Commands
+
+...
+
+### Further Reading
+
+https://bitfieldconsulting.com/posts/test-scripts
+
+https://atlasgo.io/blog/2024/09/09/how-go-tests-go-test
+
+https://encore.dev/blog/testscript-hidden-testing-gem

acceptance/acceptance_test.go

@@ -1,3 +1,5 @@
+//go:build acceptance
+
 package acceptance_test
 
 import (