tools: migrate test generation features to `gopls`

[emil14]

Is your feature request related to a problem? Please describe.
I'm always frustrated when I click on "Generate test for function" and see "No tests were generated for ...".

Describe the solution you'd like
I would like to see a reason of why there was no tests were generated. For example - "test for ... already exist".

Additional context
It would be perfect to see a location of generated tests if there is already existing one. Or after successful generation.

[n1lesh]

@stamblerre I would like to work on this if no one's working.

[stamblerre]

Sounds good! /cc @hyangah to confirm that this would be a good thing to work on

[n1lesh]

Please correct me if I'm wrong, to generate tests vscode-go calls gotests lib internally as a child process.

However, gotests doesn't return any error if test(s) don't get generated other than "No tests were generated for...". The generateTest method (from gotests) ignores the func if test is already generated for it, and returns no error.

Probably modifying gotests to return an error for existing tests would be a better idea?

[stamblerre]

@n1lesh: Thanks for digging into the underlying cause! An alternative option may actually be to move the test generation logic into gopls itself, so that we can adjust the behavior more easily. Would you be willing to work on a gopls change that adds a command to generate tests instead? I know that's a bigger ask than this fix, but I'd be happy to offer pointers if you're interested.

[n1lesh]

@stamblerre I can work on the gopls change.