Add docs for testing preview versions

docs/contributing/test_versions.md

@@ -0,0 +1,41 @@
+# Testing preview versions
+
+The kOps test infrastructure creates builds of git branches and pull requests.
+These builds can easily be used for testing. Note that these builds are cleaned up after some time, so it is not safe to use these for production clusters.
+
+This is handy as if you do not want to compile e.g the master branch to test a fix.
+
+## Testing release branches
+
+After each successful merge to a release branch, the build is made available through a release marker.
+
+| branch | marker |
+|--------|--------|
+| https://storage.googleapis.com/kops-ci/bin/latest-ci-updown-green.txt | master branch |
+| https://storage.googleapis.com/k8s-staging-kops/kops/releases/markers/release-1.21/latest-ci.txt | kOps 1.21 release branch |
+| https://storage.googleapis.com/k8s-staging-kops/kops/releases/markers/release-1.22/latest-ci.txt | kOps 1.22 release branch |
+
+You can create a cluster using these markers using the following scripts:
+
+```sh
+marker="https://storage.googleapis.com/kops-ci/bin/latest-ci-updown-green.txt"
+export KOPS_BASE_URL="$(curl -s https://storage.googleapis.com/kops-ci/bin/latest-ci-updown-green.txt)"
+wget -q "$KOPS_BASE_URL/$(go env GOOS)/$(go env GOARCH)/kops"
+chmod +x ./kops
+./kops version
+```
+
+Keep in mind you need to set `KOPS_BASE_URL` every time you use `./kops`
+
+## Testing a pull request
+
+When a PR builds successfully, you can test the PR using the following script:
+
+```sh
+pr=13208
+sha=$(curl -s -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/kubernetes/kops/pulls/${pr} | jq -r .head.sha )
+export KOPS_BASE_URL=https://storage.googleapis.com/kops-ci/pulls/pull-kops-e2e-kubernetes-aws/pull-v1.24.0-alpha.2-68-g8a1070a1b9
+wget -q "$KOPS_BASE_URL/$(go env GOOS)/$(go env GOARCH)/kops"
+chmod +x ./kops
+./kops version
+```

mkdocs.yml

@@ -140,6 +140,7 @@ nav:
     - Building: "contributing/building.md"
     - Adding a feature: "contributing/adding_a_feature.md"
     - Testing: "contributing/testing.md"
+    - Testing preview versions: "contributing/test_versions.md"
     - Developing using Docker: "contributing/Docker.md"
     - Documentation Guidelines: "contributing/documentation.md"
     - Hack Directory: "contributing/hack.md"