doc/tutorial/kubernetes: investigate issues when running CUE_UPDATE=1 go test ./...

[cueckoo]

Originally opened by @myitcv in cuelang/cue#815

Using Go 1.16 and running:

CUE_UPDATE=1 go test ./...

• All doc/tutorial/kubernetes/quick/cue.mod/gen/**/*.cue files are removed
• We don't get a test failure when it looks/feels like we should
• We still don't get a test failure when running go test ./... subsequently, despite the fact that there is a massive diff

[cueckoo]

Original reply by @myitcv in cuelang/cue#815 (comment)

Initial analysis: this appears to be related to Go 1.16. Running the above sequence with Go < 1.16 "works" in so far as the doc/tutorial/kubernetes/quick/cue.mod/gen/**/*.cue files are not removed.

[cueckoo]

Original reply by @myitcv in cuelang/cue#815 (comment)

One issue identified by this analysis was a missing go mod init step in the tutorial. That was fixed in cuelang/cue@b51368e. The issues regarding CUE_UPDATE=1 go test ./... are wider and intrinsically linked to the current tutorial setup. Fixing that setup in a sustainable way (that will also form the basis for other tutorials) is captured in cuelang/cue#824, but is not a short-term priority. Hence closing this issue, as there is no longer an immediate pre-v0.3.0 problems to solve with respect to the K8s tutorial.