Improve reporting of tests coverage

[skosito]

Describe the Issue

Currently, for packages without any _test.go file, go test reports [no-test-files] and coverage is not included at all (eg. common/bitcoin package, not present in codecov report, because there are no tests, latest develop report: https://app.codecov.io/gh/zeta-chain/node/tree/develop/common). Reason for this is that packages that are without test files are not included in coverage.out which is uploaded to codecov.

Expected Outcome

These type of packages should be reported with 0% coverage, so they are detected and included in overall coverage, otherwise coverage is not correct.

Details

There are a lot of details in this issue: golang/go#24570 and it seems that this works as expected in go1.22 https://tip.golang.org/doc/go1.22#tools where 0% coverage is reported instead. But for now we can do the following (summary from various github issues):

• prefered solution: add empty _test.go file in packages that are reported with [no test files] and we want to include in the coverage, for example adding empty _test.go file in common/bitcoin package shows it in the coverage.
  While this is not super clean, it seems like the most accurate solution (also recommended throughout this issue, some projects even implemented CI to automatically add this).

• use -coverpkg=./... option with go test - from docs:

Apply coverage analysis in each test to packages matching the patterns.
The default is for each test to analyze only the package being tested.

This kinda works, but not quite. If package doesn't contain any test, but test of some other package calls it, it will still be covered. Eg:
common/chain.go function IsHeaderSupportedEvmChain is not covered with unit tests in common package, but because it is called in message_add_block_header.go, which has tests, it is also reported as covered when this flag is used. This is not correct in context of unit tests coverage, where each package that is reporting coverage is expected to have its own tests.

Also, it doesn't solve the problem completely - if package is not referenced in any test, it still won't be included in coverage.

Furthermore, this flag has multiple bugs after go1.19, which is solved by using GOEXPERIMENT=nocoverageredesign (different coverage results are reported with and without this flag: golang/go#58770 and it is confirmed locally).

[lumtis]

prefered solution: add empty _test.go file in packages that are reported with [no test files] and we want to include in the coverage, for example adding empty _test.go file in common/bitcoin package shows it in the coverage.
While this is not super clean, it seems like the most accurate solution (also recommended throughout this issue, some projects even implemented CI to automatically add this).

Any drawback on this solution? It seems trivial and also I don't think cleanliness is a concerns, we need to add the tests so good thing to add a placeholder

[skosito]

prefered solution: add empty _test.go file in packages that are reported with [no test files] and we want to include in the coverage, for example adding empty _test.go file in common/bitcoin package shows it in the coverage.
While this is not super clean, it seems like the most accurate solution (also recommended throughout this issue, some projects even implemented CI to automatically add this).

Any drawback on this solution? It seems trivial and also I don't think cleanliness is a concerns, we need to add the tests so good thing to add a placeholder

I dont think there are any drawbacks, it should be straightforward. Probably can be added manually now, and for future if new package is added without any test files, codecov PR check should catch it, so we dont need any additional CI checks for this?

[lumtis]

I dont think there are any drawbacks, it should be straightforward. Probably can be added manually now, and for future if new package is added without any test files, codecov PR check should catch it, so we dont need any additional CI checks for this?

We should prevent in our code reviews to let someone add a new package without any tests