We're deprecating providertest.NewProviderTest, so use the new
pulumitest based approach instead.
- Update test code to use PreviewProviderUpgrade.
- Use provider attachment instead of the bin directory.
- Rename state.json to stack.json & let the first run migrate the stack
to a stable, non-machine dependent name.
* Rename the provider to dockerbuild.
* Add Makefile targets required by CI.
* Add per-language test targets compatible with CI.
* Fix broken example yaml.
* Add gitignore exclusions to fix SDK generation in CI.
* Fix lint errors.
* Vendor pulumi CLI via `tools.go` instead of `.pulumi`.
* Consolidate `go.mod`s into one file, with a minimal `go.mod` for the
Go SDK.
* Add codecov.
