Krew upgrade needs integration test

[corneliusweig]

Krew upgrade is currently not covered by integration tests, because it requires a more advanced test setup. What the integration test should do:

• Install an old plugin version
• Verify that the old version is installed
• Run krew upgrade
• Verify that the new version is installed

The tricky part is to reliably get two plugin versions in the test. One way to do this, could be to install a fixture version with the --manifest option. To verify that the original version and the eventual version are actually different, one could take the hash of a file that must change during upgrade.

[ahmetb]

Yeah, we'd need --manifest because krew upgrade calls krew update internally, which would undo if you were overwriting the manifest file in the index.

We'd just need to vendor the old file into testdata/ and keep it up-to-date (compliant with the current version).

/kind bug
/priority important-soon

[corneliusweig]

/assign